# Source code for spacepy.pycdf.istp

    #!/usr/bin/env python

    """Support for ISTP-compliant CDFs

    The `ISTP metadata standard  <https://spdf.gsfc.nasa.gov/sp_use_of_cdf.html>`_
    specifies the interpretation of the attributes in a CDF to describe
    relationships between the variables and their physical interpretation.

    This module supports that subset of CDFs.

    Authors: Jon Niehof

    Additional Contributors: Lorna Ellis, Asher Merrill

    Institution: University of New Hampshire

    Contact: Jonathan.Niehof@unh.edu

    .. rubric:: Classes

    .. autosummary::
        :toctree:
        :template: clean_class.rst

        FileChecks
        VarBundle
        VariableChecks

    .. rubric:: Functions

    .. autosummary::
        :toctree:

        fillval
        format
        nanfill
    """

    import collections
    import datetime
    import functools
    import inspect
    import itertools
    import math
    import os.path
    import re

    import numpy
    import spacepy.datamodel
    import spacepy.pycdf
    import spacepy.pycdf.const

    class VariableChecks(object):
        """ISTP compliance checks for a single variable.

        Checks a variable's compliance with ISTP standards. This mostly
        performs checks that are not currently performed by the `ISTP
        skeleton editor <https://spdf.gsfc.nasa.gov/skteditor/>`_.  All
        tests return a list, one error string for every noncompliance
        found (empty list if compliant). :meth:`all` will perform all
        tests and concatenate all errors.

        .. autosummary::

            all
            deltas
            depends
            depsize
            empty_entry
            fieldnam
            fillval
            recordcount
            validdisplaytype
            validrange
            validscale

        .. automethod:: all
        .. automethod:: deltas
        .. automethod:: depends
        .. automethod:: depsize
        .. automethod:: empty_entry
        .. automethod:: fieldnam
        .. automethod:: fillval
        .. automethod:: recordcount
        .. automethod:: validdisplaytype
        .. automethod:: validrange
        .. automethod:: validscale

        """
        #When adding new tests, add to list above
        #Validation failures should be formatted as a sentence (initial cap,
        #closing period) and NOT include the variable name.

        @classmethod
        def all(cls, v, catch=False):
            """Perform all variable tests

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check
            catch : bool
                Catch exceptions in tests (default False). If True, any
                exceptions in subtests will result in an addition to the
                validation failures of the form "Test x did not complete."
                Calling the individual test will reveal the full traceback.

            Returns
            -------
            list of str
                Description of each validation failure.

            Examples
            --------
            >>> import spacepy.pycdf
            >>> import spacepy.pycdf.istp
            >>> f = spacepy.pycdf.CDF('foo.cdf', create=True)
            >>> v = f.new('Var', data=[1, 2, 3])
            >>> spacepy.pycdf.istp.VariableChecks.all(v)
            ['No FIELDNAM attribute.']
            """
            callme = [func for name, func in inspect.getmembers(cls)
                      if not name.startswith('_') and not name.endswith('_')
                      and callable(func) and name != 'all']
            errors = []
            for f in callme:
                try:
                    errors.extend(f(v))
                except:
                    if catch:
                        errors.append('Test {} did not complete.'.format(
                            f.__name__))
                    else:
                        raise
            return errors

        @classmethod
        def depends(cls, v):
            """Checks that DELTA, DEPEND, and LABL_PTR variables exist

            Check that variables specified in the variable attributes for
            `DELTA
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#DELTA>`_,
            `DEPEND
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#DEPEND_0>`_,
            and `LABL_PTR
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#LABL_PTR_1>`_
            exist in the CDF.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            return ['{} variable {} missing.'.format(a, v.attrs[a])
                    for a in v.attrs
                    if (a.startswith(('DEPEND_', 'LABL_PTR_',))
                        or a in ('DELTA_PLUS_VAR', 'DELTA_MINUS_VAR'))
                    and not v.attrs[a] in v.cdf_file]

        @classmethod
        def deltas(cls, v):
            """Check DELTA variables

            Check that variables specified in the variable attributes for
            `DELTA
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#DELTA>`_
            match the type, size, and units of this variable.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            errs = []
            if v.rv():
                shape = v.shape[1:]
                n_recs = len(v)
            else:
                shape = v.shape
                n_recs = None
            for delta in ('DELTA_PLUS_VAR', 'DELTA_MINUS_VAR'):
                if not delta in v.attrs:
                    continue
                deltavar = v.cdf_file[v.attrs[delta]]
                if deltavar.type() != v.type():
                    errs.append(
                        '{} type {} does not match variable type {}.'.format(
                            delta, spacepy.pycdf.lib.cdftypenames[deltavar.type()],
                            spacepy.pycdf.lib.cdftypenames[v.type()]))
                if deltavar.attrs.get('UNITS', None) != v.attrs.get('UNITS', None):
                    errs.append('{} units do not match variable units.'.format(
                        delta))
                if deltavar.rv():
                    dshape = deltavar.shape[1:]
                    d_n_recs = len(deltavar)
                else:
                    dshape = deltavar.shape
                    d_n_recs = None
                if dshape != shape:
                    errs.append(
                        '{} shape {} does not match variable shape {}.'.format(
                            delta, dshape, shape))
                if d_n_recs is not None and n_recs is not None \
                   and d_n_recs != n_recs:
                    errs.append((
                        '{} record count {} does not match variable record'
                        ' count {}.').format(
                            delta, d_n_recs, n_recs))
            return errs

        @classmethod
        def depsize(cls, v):
            """Checks that DEPEND has same shape as that dim

            Compares the size of variables specified in the variable
            attributes for `DEPEND
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#DEPEND_0>`_
            and compares to the size of the corresponding dimension in
            this variable.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            rv = int(v.rv()) #RV is a leading dimension
            errs = []
            # Check that don't have invalid DEPEND_1
            if v.shape == (0,):
                if 'DEPEND_1' in v.attrs or 'DEPEND_2' in v.attrs:
                    errs.append('Do not expect DEPEND_1 or DEPEND_2 in 1 dimensional variable.')
            for i in range(rv, len(v.shape)): #This is index on shape (of var)
                depidx = i + 1 - rv #This is x in  DEPEND_x
                target = v.shape[i]
                if not 'DEPEND_{}'.format(depidx) in v.attrs:
                    continue
                d = v.attrs['DEPEND_{}'.format(depidx)]
                if d in v.cdf_file:
                    dv = v.cdf_file[d]
                else:
                    continue #this is a different error
                if dv.rv() != ('DEPEND_0' in dv.attrs):
                    errs.append('DEPEND_{} {} is RV but has no DEPEND_0.'
                                .format(depidx, d))
                    continue
                #We hope the only weirdness is whether the dependency
                #is constant, or dependent on record. If it's dependent
                #on another dependency, this gets really weird really fast
                # If the dependency is dependent, remove the lower level
                # dependency size from consideration
                # eg. if counts [80,48], depends on energy [80,48],
                # depends on look [80], remove 80 from the view of energy
                # so that we accurately check 48==48.
                # NB: This assumes max of two layers of dependency
                if 'DEPEND_2' in dv.attrs:
                    errs.append('Do not expect three layers of dependency.')
                    continue
                elif 'DEPEND_1' in dv.attrs:
                    dd = dv.attrs['DEPEND_1']
                    if dd in v.cdf_file:
                        ddv = v.cdf_file[dd]
                    else:
                        continue #this is a different error
                    actual = list(dv.shape)
                    for ii in actual:
                        if ii in ddv.shape:
                            actual.remove(ii)
                    if 'DEPEND_0' in dv.attrs:
                        # record varying
                        dd = dv.attrs['DEPEND_0']
                        if dd[:5] != 'Epoch':
                            errs.append('Expect DEPEND_0 to be Epoch.')
                            continue
                        if dd in v.cdf_file:
                            ddv = v.cdf_file[dd]
                        else:
                            continue #this is a different error
                        for ii in actual:
                            if ii in ddv.shape:
                                actual.remove(ii)

                    if len(actual) != 1:
                        errs.append('More complicated double dependency than taken into account.')
                        continue
                    else:
                        actual = actual[0]
                else:
                    actual = dv.shape[int(dv.rv())]
                if target != actual:
                    errs.append('Dim {} sized {} but DEPEND_{} {} sized {}.'.format(
                        i, target, depidx, d, actual))

            return errs

        @classmethod
        def empty_entry(cls, v):
            """Check for attributes with empty string

            Checks attributes for this variable for any entries consisting
            of an empty string. These should be replaced with a single space.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.
            """
            errs = []
            for a in v.attrs:
                if v.attrs.type(a) in (spacepy.pycdf.const.CDF_CHAR.value,
                                       spacepy.pycdf.const.CDF_UCHAR.value) \
                    and v.attrs[a] == '':
                    errs.append('Empty CHAR entry for attribute {}.'.format(a))
            return errs

        @classmethod
        def fillval(cls, v):
            """Check for FILLVAL presence, type, value

            Checks variable for existence of `FILLVAL
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#FILLVAL>`_
            attribute and makes sure it is the same type as variable and matches
            ISTP value.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            See Also
            --------
            spacepy.pycdf.istp.fillval : Automatic setting of this value.
            """
            errs = []
            if not 'FILLVAL' in v.attrs:
                return ['No FILLVAL attribute.']
            if v.attrs.type('FILLVAL') != v.type():
                errs.append(
                    'FILLVAL type {} does not match variable type {}.'.format(
                        spacepy.pycdf.lib.cdftypenames[v.attrs.type('FILLVAL')],
                        spacepy.pycdf.lib.cdftypenames[v.type()]))
            expected = fillval(v, ret=True)
            timetype = v.type() in spacepy.pycdf.lib.timetypes
            actual = (v.cdf_file.raw_var(v.name()) if timetype else v)\
                     .attrs['FILLVAL']
            # isclose added in numpy 1.7, so fix this when go to 0.3.0
            if hasattr(numpy, 'isclose'):
                match = numpy.isclose(
                    actual, expected, atol=0, rtol=1e-7)\
                    if numpy.issubdtype(v.dtype, numpy.floating)\
                    else numpy.all(actual == expected)
            else:
                if numpy.issubdtype(v.dtype, numpy.floating):
                    match = (abs(actual - expected) / expected < 1e-7)
                else:
                    match = numpy.all(actual == expected)
            if not match:
                if timetype:
                    converted_expected = {
                        spacepy.pycdf.const.CDF_EPOCH.value:
                        spacepy.pycdf.lib.v_epoch_to_datetime,
                        spacepy.pycdf.const.CDF_EPOCH16.value:
                        spacepy.pycdf.lib.v_epoch16_to_datetime,
                        spacepy.pycdf.const.CDF_TIME_TT2000.value:
                        spacepy.pycdf.lib.v_tt2000_to_datetime
                    }[v.type()](expected)
                    errs.append(
                        'FILLVAL {} ({}), should be {} ({}) for variable type {}.'
                        .format(
                            actual,
                            v.attrs['FILLVAL'],
                            expected,
                            converted_expected,
                            spacepy.pycdf.lib.cdftypenames[v.type()]))
                else:
                    errs.append(
                        'FILLVAL {}, should be {} for variable type {}.'.format(
                            actual, expected,
                            spacepy.pycdf.lib.cdftypenames[v.type()]))
            return errs

        @classmethod
        def recordcount(cls, v):
            """Check that the DEPEND_0 has same record count as variable

            Checks the record count of the variable specified in the
            variable attribute for `DEPEND_0
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#DEPEND_0>`_
            and compares to the record count for this variable.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            if not v.rv() or not 'DEPEND_0' in v.attrs:
                return []
            dep0 = v.attrs['DEPEND_0']
            if not dep0 in v.cdf_file: #This is a DIFFERENT error
                return []
            if len(v) != len(v.cdf_file[dep0]):
                return ['{} records; DEPEND_0 {} has {}.'.format(
                    len(v), dep0, len(v.cdf_file[dep0]))]
            return []

        @classmethod
        def _validhelper(cls, v, rng=True):
            """Helper function for checking SCALEMIN/MAX, VALIDMIN/MAX

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            rng : bool
                Do range check (True, default) or scale check (False)

            Returns
            -------
            list of str
                Description of each validation failure.
            """
            validscale = 'VALID' if rng else 'SCALE'
            whichmin, whichmax = ('VALIDMIN', 'VALIDMAX') if rng \
                                 else ('SCALEMIN', 'SCALEMAX')
            errs = []
            vshape = v.shape
            minval, maxval = spacepy.pycdf.lib.get_minmax(v.type())
            if rng:
                data = v[...]
                is_fill = False
                if 'FILLVAL' in v.attrs:
                    filldtype = spacepy.pycdf.lib.numpytypedict.get(
                        v.attrs.type('FILLVAL'), object)
                    if numpy.issubdtype(v.dtype, numpy.floating) \
                       and numpy.issubdtype(filldtype, numpy.floating):
                        is_fill = numpy.isclose(data, v.attrs['FILLVAL'])
                    elif numpy.can_cast(numpy.asanyarray(v.attrs['FILLVAL']),
                                        v.dtype):
                        is_fill = data == v.attrs['FILLVAL']
            for which in (whichmin, whichmax):
                if not which in v.attrs:
                    continue
                if v.attrs.type(which) != v.type():
                    errs.append(
                        '{} type {} does not match variable type {}.'.format(
                            which,
                            spacepy.pycdf.lib.cdftypenames[v.attrs.type(which)],
                            spacepy.pycdf.lib.cdftypenames[v.type()]))
                attrval = v.attrs[which]
                multidim = bool(numpy.shape(attrval)) #multi-dimensional
                if multidim: #Compare shapes, require only 1D var
                    #Match attribute dim to first non-record var dim
                    firstdim = int(v.rv())
                    if vshape[firstdim] != numpy.shape(attrval)[0]:
                        errs.append(('{} element count {} does not match first data'
                                     ' dimension size {}.').format(
                                         which, numpy.shape(attrval)[0],
                                         v.shape[firstdim]))
                        continue
                    if len(vshape) != firstdim + 1: #only one non-record dim
                        errs.append('Multi-element {} only valid with 1D variable.'
                                    .format(which))
                        continue
                    if firstdim: #Add pseudo-record dim
                        attrval = numpy.reshape(attrval, (1, -1))
                # min, max, variable data all same dtype
                if not numpy.can_cast(numpy.asanyarray(attrval),
                                      numpy.asanyarray(minval).dtype):
                    errs.append(
                        '{} type {} not comparable to variable type {}.'.format(
                            which,
                            spacepy.pycdf.lib.cdftypenames[v.attrs.type(which)],
                            spacepy.pycdf.lib.cdftypenames[v.type()]
                        ))
                    continue # Cannot do comparisons
                if numpy.any((minval > attrval)) or numpy.any((maxval < attrval)):
                    errs.append('{} ({}) outside valid data range ({},{}).'.format(
                        which, attrval[0, :] if multidim else attrval,
                        minval, maxval))
                if not rng or not len(v): #nothing to compare
                    continue
                #Always put numpy array on the left so knows to do element compare
                idx = (data < attrval) if which == whichmin \
                      else (data > attrval)
                idx = numpy.logical_and(idx, numpy.logical_not(is_fill))
                if idx.any():
                    direction = 'under' if which == whichmin else 'over'
                    if len(vshape) == 0: #Scalar
                        errs.append('Value {} {} {} {}.'.format(
                            data, direction, which,
                            attrval[0, :] if multidim else attrval))
                        continue
                    badidx = numpy.nonzero(idx)
                    badvals = data[badidx]
                    if len(badidx) > 1: #Multi-dimensional data
                        badidx = numpy.transpose(badidx) #Group by value not axis
                    else:
                        badidx = badidx[0] #Just recover the index value
                    if len(badvals) < 10:
                        badvalstr = ', '.join(str(d) for d in badvals)
                        badidxstr = ', '.join(str(d) for d in badidx)
                        errs.append('Value {} at index {} {} {} {}.'.format(
                            badvalstr, badidxstr,
                            direction, which,
                            attrval[0, :] if multidim else attrval))
                    else:
                        errs.append('{} values {} {} {}'.format(
                            len(badvals), direction, which,
                            attrval[0, :] if multidim else attrval))
            if (whichmin in v.attrs) and (whichmax in v.attrs):
                if numpy.any(v.attrs[whichmin] > v.attrs[whichmax]):
                    errs.append('{} > {}.'.format(whichmin, whichmax))
            return errs

        @classmethod
        def validrange(cls, v):
            """Check that all values are within VALIDMIN/VALIDMAX, or FILLVAL

            Compare all values of this variable to `VALIDMIN
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#VALIDMIN>`_
            and ``VALIDMAX``; fails validation if any values are below
            VALIDMIN or above ``VALIDMAX`` unless equal to `FILLVAL
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#FILLVAL>`_.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            return cls._validhelper(v)

        @classmethod
        def validscale(cls, v):
            """Check SCALEMIN<=SCALEMAX, and both in range for CDF datatype.

            Compares `SCALEMIN
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#SCALEMIN>`_
            to ``SCALEMAX`` to make sure it isn't larger and both are
            within range of the variable CDF datatype.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            return cls._validhelper(v, False)

        @classmethod
        def validdisplaytype(cls, v):
            """Check that plottype matches dimensions.

            Check `DISPLAYTYPE
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#DISPLAY_TYPE>`_
            of this variable and makes sure it is reasonable for the
            variable dimensions.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            time_st = 'time_series'
            spec_st = 'spectrogram'
            errs = []
            if 'DISPLAY_TYPE' in v.attrs:
                if (len(v.shape) == 1) and (v.attrs['DISPLAY_TYPE'] != time_st):
                    errs.append('1 dim variable with {} display type.'.format(
                        v.attrs['DISPLAY_TYPE']))
                elif (len(v.shape) > 1) and (v.attrs['DISPLAY_TYPE'] != spec_st):
                    errs.append('Multi dim variable with {} display type.'.format(
                        v.attrs['DISPLAY_TYPE']))
            return errs

        @classmethod
        def fieldnam(cls, v):
            """Check that FIELDNAM attribute matches variable name.

            Compare `FIELDNAM
            <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#FIELDNAM>`_
            attribute to the variable name; fail validation if they don't
            match.

            Parameters
            ----------
            v : :class:`~spacepy.pycdf.Var`
                Variable to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            errs = []
            vname = v.name()
            if 'FIELDNAM' not in v.attrs:
                errs.append('No FIELDNAM attribute.')
            elif v.attrs['FIELDNAM'] != vname:
                errs.append('FIELDNAM attribute {} does not match var name.'
                            .format(v.attrs['FIELDNAM']))
            return errs

    class FileChecks(object):
        """ISTP compliance checks for a CDF file.

        Checks a file's compliance with ISTP standards. This mostly
        performs checks that are not currently performed by the `ISTP
        skeleton editor <https://spdf.gsfc.nasa.gov/skteditor/>`_.  All
        tests return a list, one error string for every noncompliance
        found (empty list if compliant). :meth:`all` will perform all
        tests and concatenate all errors.

        .. autosummary::

            all
            empty_entry
            filename
            time_monoton
            times

        .. automethod:: all
        .. automethod:: empty_entry
        .. automethod:: filename
        .. automethod:: time_monoton
        .. automethod:: times

        """
        #When adding new tests, add to list above.
        #Validation failures should be formatted as a sentence (initial cap,
        #closing period).

        @classmethod
        def all(cls, f, catch=False):
            """Perform all variable and file-level tests

            In addition to calling every test in this class, will also call
            :meth:`VariableChecks.all` for every variable in the file.

            Parameters
            ----------
            f : :class:`~spacepy.pycdf.CDF`
                Open CDF file to check
            catch : bool
                Catch exceptions in tests (default False). If True, any
                exceptions in subtests will result in an addition to the
                validation failures of the form "Test x did not complete."
                Calling the individual test will reveal the full traceback.

            Returns
            -------
            list of str
                Description of each validation failure.

            Examples
            --------
            >>> import spacepy.pycdf
            >>> import spacepy.pycdf.istp
            >>> f = spacepy.pycdf.CDF('foo.cdf', create=True)
            >>> v = f.new('Var', data=[1, 2, 3])
            >>> spacepy.pycdf.istp.FileChecks.all(f)
            ['No Logical_source in global attrs.',
            'No Logical_file_id in global attrs.',
            'Cannot parse date from filename foo.cdf.',
            'Var: No FIELDNAM attribute.']
            """
            #Update this list when adding new test functions
            callme = [func for name, func in inspect.getmembers(cls)
                      if not name.startswith('_') and not name.endswith('_')
                      and callable(func) and name != 'all']
            errors = []
            for func in callme:
                try:
                    errors.extend(func(f))
                except:
                    if catch:
                        errors.append('Test {} did not complete.'.format(
                            func.__name__))
                    else:
                        raise

            for v in f:
                errors.extend(('{}: {}'.format(v, e)
                               for e in VariableChecks.all(f[v], catch=catch)))
            return errors

        @classmethod
        def empty_entry(cls, f):
            """Check for attributes with empty string

            Checks global attributes for this variable for any entries consisting
            of an empty string. These should be replaced with a single space.

            Parameters
            ----------
            f : :class:`~spacepy.pycdf.CDF`
                Open CDF file to check

            Returns
            -------
            list of str
                Description of each validation failure.
            """
            errs = []
            for a in f.attrs:
                attr = f.attrs[a]
                for i in range(attr.max_idx() + 1):
                    if attr.has_entry(i) \
                        and attr.type(i) in (spacepy.pycdf.const.CDF_CHAR.value,
                                             spacepy.pycdf.const.CDF_UCHAR.value) \
                        and attr[i] == '':
                        errs.append('Empty CHAR entry {} for attribute {}.'
                                    .format(i, a))
            return errs

        @classmethod
        def filename(cls, f):
            """Compare filename to global attributes

            Check global attribute `Logical_file_id
            <https://spdf.gsfc.nasa.gov/istp_guide/gattributes.html#Logical_file_id>`_
            and `Logical_source
            <https://spdf.gsfc.nasa.gov/istp_guide/gattributes.html#Logical_source>`_
            for consistency with CDF filename.

            Parameters
            ----------
            f : :class:`~spacepy.pycdf.CDF`
                Open CDF file to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            errs = []
            for a in ('Logical_source', 'Logical_file_id'):
                if not a in f.attrs or len(f.attrs[a]) == 0:
                    errs.append('No {} in global attrs.'.format(a))
            if errs:
                return errs
            fname = os.path.basename(f.pathname)
            if not bytes is str:
                fname = fname.decode('ascii')
            if not fname.startswith(f.attrs['Logical_source'][0]):
                errs.append("Logical_source {} doesn't match filename {}.".format(
                    f.attrs['Logical_source'][0], fname))
            if fname[:-4] != f.attrs['Logical_file_id'][0]:
                errs.append("Logical_file_id {} doesn't match filename {}.".format(
                    f.attrs['Logical_file_id'][0], fname))
            return errs

        @classmethod
        def time_monoton(cls, f):
            """Checks that times are monotonic

            Check that all `Epoch
            <https://spdf.gsfc.nasa.gov/istp_guide/variables.html#support_data_eg1>`_
            variables are monotonically increasing.

            Parameters
            ----------
            f : :class:`~spacepy.pycdf.CDF`
                Open CDF file to check

            Returns
            -------
            list of str
                Description of each validation failure.

            """
            errs = []
            for v in f:
                if not f[v].type() in (spacepy.pycdf.const.CDF_EPOCH.value,
                                       spacepy.pycdf.const.CDF_EPOCH16.value,
                                       spacepy.pycdf.const.CDF_TIME_TT2000.value):
                    continue
                data = f[v][...]
                idx = numpy.where(numpy.diff(data) < datetime.timedelta(0))[0]
                if not any(idx):
                    continue
                errs.append('{}: Nonmonotonic time at record {}.'.format(
                    v, ', '.join((str(i) for i in (idx + 1)))))
            return errs

        @classmethod
        def times(cls, f):
            """Compare filename to times

            Check that all `Epoch
            <https://spdf.gsfc.nasa.gov/istp_guide/variables.html#support_data_eg1>`_
            variables only contain times matching filename.

            Parameters
            ----------
            f : :class:`~spacepy.pycdf.CDF`
                Open CDF file to check

            Returns
            -------
            list of str
                Description of each validation failure.

            Notes
            -----
            This function assumes daily files and should be extended based on the
            File_naming_convention global attribute (which itself is another good
            check to have.)

            """
            errs = []
            fname = os.path.basename(f.pathname)
            if not bytes is str:
                fname = fname.decode('ascii')
            m = re.search('\d{8}', fname)
            if not m:
                return ['Cannot parse date from filename {}'.format(fname)]
            datestr = m.group(0)
            for v in f:
                if f[v].type() in (spacepy.pycdf.const.CDF_EPOCH.value,
                                   spacepy.pycdf.const.CDF_EPOCH16.value,
                                   spacepy.pycdf.const.CDF_TIME_TT2000.value):
                    datestrs = list(set((d.strftime('%Y%m%d') for d in f[v][...])))
                    if len(datestrs) == 0:
                        continue
                    elif len(datestrs) > 1:
                        errs.append('{}: multiple days {}.'.format(
                            v, ', '.join(sorted(datestrs))))
                    elif datestrs[0] != datestr:
                        errs.append('{}: date {} doesn\'t match file {}.'.format(
                            v, datestrs[0], fname))
            return errs

    def fillval(v, ret=False):
        """Set ISTP-compliant FILLVAL on a variable

        Sets or returns a CDF variable's `FILLVAL
        <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#FILLVAL>`_
        attribute to the value required by ISTP (based on variable type).

        Parameters
        ----------
        v : :class:`~spacepy.pycdf.Var`
            CDF variable to update

        Other Parameters
        ----------------
        ret : boolean
            If True, return the value instead of setting it (Default False, set).

        Returns
        -------
        various
            If ``ret`` is True, returns the correct value for variable type (which
            may be of various Python types).  Otherwise sets the value and returns
            ``None``.

        Examples
        --------
        >>> import spacepy.pycdf
        >>> import spacepy.pycdf.istp
        >>> f = spacepy.pycdf.CDF('foo.cdf', create=True)
        >>> v = f.new('Var', data=[1, 2, 3])
        >>> spacepy.pycdf.istp.fillval(v)
        >>> v.attrs['FILLVAL']
        -128
        """
        #Fill value, indexed by the CDF type (numeric)
        fillvals = {}
        #Integers
        for i in (1, 2, 4, 8):
            fillvals[getattr(spacepy.pycdf.const, 'CDF_INT{}'.format(i)).value] = \
                - 2 ** (8*i - 1)
            if i == 8:
                continue
            fillvals[getattr(spacepy.pycdf.const, 'CDF_UINT{}'.format(i)).value] = \
                2 ** (8*i) - 1
        fillvals[spacepy.pycdf.const.CDF_EPOCH16.value] = (-1e31, -1e31)
        fillvals[spacepy.pycdf.const.CDF_REAL8.value] = -1e31
        fillvals[spacepy.pycdf.const.CDF_REAL4.value] = -1e31
        fillvals[spacepy.pycdf.const.CDF_CHAR.value] = ' '
        fillvals[spacepy.pycdf.const.CDF_UCHAR.value] = ' '
        #Equivalent pairs
        for cdf_t, equiv in (
                (spacepy.pycdf.const.CDF_TIME_TT2000, spacepy.pycdf.const.CDF_INT8),
                (spacepy.pycdf.const.CDF_EPOCH, spacepy.pycdf.const.CDF_REAL8),
                (spacepy.pycdf.const.CDF_BYTE, spacepy.pycdf.const.CDF_INT1),
                (spacepy.pycdf.const.CDF_FLOAT, spacepy.pycdf.const.CDF_REAL4),
                (spacepy.pycdf.const.CDF_DOUBLE, spacepy.pycdf.const.CDF_REAL8),
        ):
            fillvals[cdf_t.value] = fillvals[equiv.value]
        value = fillvals[v.type()]
        if ret:
            return value
        if 'FILLVAL' in v.attrs:
            del v.attrs['FILLVAL']
        v.attrs.new('FILLVAL', data=value, type=v.type())

    def format(v, use_scaleminmax=False, dryrun=False):
        """Set ISTP-compliant FORMAT on a variable

        Sets a CDF variable's `FORMAT
        <https://spdf.gsfc.nasa.gov/istp_guide/vattributes.html#FORMAT>`_
        attribute, which provides a Fortran-like format string that should
        be useable for printing any valid value in the variable. Sets
        according to the VALIDMIN/VALIDMAX attributes (or, optionally,
        SCALEMIN/SCALEMAX) if present, otherwise uses the full range of
        the type.

        Parameters
        ----------
        v : :class:`~spacepy.pycdf.Var`
            Variable to update
        use_scaleminmax : bool, optional
            Use SCALEMIN/MAX instead of VALIDMIN/MAX (default False).
            Note: istpchecks may complain about result.
        dryrun : bool, optional
            Print the decided format to stdout instead of modifying
            the CDF (for use in command-line debugging) (default False).

        Examples
        --------
        >>> import spacepy.pycdf
        >>> import spacepy.pycdf.istp
        >>> f = spacepy.pycdf.CDF('foo.cdf', create=True)
        >>> v = f.new('Var', data=[1, 2, 3])
        >>> spacepy.pycdf.istp.format(v)
        >>> v.attrs['FORMAT']
        'I4'

        """
        if use_scaleminmax:
            minn = 'SCALEMIN'
            maxx = 'SCALEMAX'
        else:
            minn = 'VALIDMIN'
            maxx = 'VALIDMAX'
        cdftype = v.type()
        if cdftype in (spacepy.pycdf.const.CDF_INT1.value,
                       spacepy.pycdf.const.CDF_INT2.value,
                       spacepy.pycdf.const.CDF_INT4.value,
                       spacepy.pycdf.const.CDF_INT8.value,
                       spacepy.pycdf.const.CDF_UINT1.value,
                       spacepy.pycdf.const.CDF_UINT2.value,
                       spacepy.pycdf.const.CDF_UINT4.value,
                       spacepy.pycdf.const.CDF_BYTE.value):
            if minn in v.attrs: #Just use validmin or scalemin
                minval = v.attrs[minn]
            elif cdftype in (spacepy.pycdf.const.CDF_UINT1.value,
                             spacepy.pycdf.const.CDF_UINT2.value,
                             spacepy.pycdf.const.CDF_UINT4.value): #unsigned, easy
                minval = 0
            elif cdftype == spacepy.pycdf.const.CDF_BYTE.value:
                minval = - 2 ** 7
            else: #Signed, harder
                size = next((i for i in (1, 2, 4, 8) if getattr(
                    spacepy.pycdf.const, 'CDF_INT{}'.format(i)).value == cdftype))
                minval = - 2 ** (8*size  - 1)
            if maxx in v.attrs: #Just use max
                maxval = v.attrs[maxx]
            elif cdftype == spacepy.pycdf.const.CDF_BYTE.value:
                maxval = 2 ** 7 - 1
            else:
                size = next((8 * i for i in (1, 2, 4) if getattr(
                    spacepy.pycdf.const, 'CDF_UINT{}'.format(i)).value == cdftype),
                            None)
                if size is None:
                    size = next((8 * i for i in (1, 2, 4, 8) if getattr(
                        spacepy.pycdf.const, 'CDF_INT{}'.format(i)).value ==
                                 cdftype)) - 1
                maxval = 2 ** size - 1
            #Two tricks:
            #-Truncate and add 1 rather than ceil so get
            #powers of 10 (log10(10) = 1 but needs two digits)
            #-Make sure not taking log of zero
            if minval < 0: #Need an extra space for the negative sign
                fmt = 'I{}'.format(int(math.log10(max(
                    abs(maxval), abs(minval), 1))) + 2)
            else:
                fmt = 'I{}'.format(int(
                    math.log10(maxval) if maxval != 0 else 1) + 1)
        elif cdftype == spacepy.pycdf.const.CDF_TIME_TT2000.value:
            fmt = 'A{}'.format(len('9999-12-31T23:59:59.999999999'))
        elif cdftype == spacepy.pycdf.const.CDF_EPOCH16.value:
            fmt = 'A{}'.format(len('31-Dec-9999 23:59:59.999.999.000.000'))
        elif cdftype == spacepy.pycdf.const.CDF_EPOCH.value:
            fmt = 'A{}'.format(len('31-Dec-9999 23:59:59.999'))
        elif cdftype in (spacepy.pycdf.const.CDF_REAL8.value,
                         spacepy.pycdf.const.CDF_REAL4.value,
                         spacepy.pycdf.const.CDF_FLOAT.value,
                         spacepy.pycdf.const.CDF_DOUBLE.value):
            # Prioritize SCALEMIN/MAX to find the number of decimals to include
            if 'SCALEMIN' in v.attrs and 'SCALEMAX' in v.attrs:
                range = v.attrs['SCALEMAX'] - v.attrs['SCALEMIN']
            # If not, use VALIDMIN/MAX
            elif 'VALIDMIN' in v.attrs and 'VALIDMAX' in v.attrs:
                range = v.attrs['VALIDMAX'] - v.attrs['VALIDMIN']
            # If not, just use nothing.
            else:
                range = None
            # Find how many spaces we need for the 'integer' part of the number
            # (Use maxx-minn for this...effectively uses VALIDMIN/MAX for most
            # cases.)
            if range and (minn in v.attrs and maxx in v.attrs):
                if len(str(int(v.attrs[maxx]))) >=\
                   len(str(int(v.attrs[minn]))):
                    ln = str(int(v.attrs[maxx]))
                else:
                    ln = str(int(v.attrs[minn]))
            if range and ln and range < 0: # Cover all our bases:
                # raise ValueError('Range ({} - {}) cannot be negative:'
                    # '\nVarname: {}\nRange: {}'.format(maxx, minn, v, range))
                ### Instead of throwing an error, just use None
                # There are old cases that for some reason have negative ranges, so
                # this is really more of a compatibility choice than a good
                # decision.
                range = None
            # All of the lengths below (the +4, +3, +2, etc...) should be EXACTLY
            # enough.  Consider adding 1, (4+1=5, 3+1=4, etc...) to possibly make
            # this easier.
            # elif range and ln and range <= 11: # If range <= 11, we want 2 decimal places:
            if range and ln and range <= 11: # If range <= 11, we want 2 decimal places:
                # Need extra for '.', and 3 decimal places (4 extra)
                fmt = 'F{}.3'.format(len([i for i in ln]) + 4)
            elif range and ln and 11 < range <= 101:
                # Need extra for '.' (1 extra)
                fmt = 'F{}.2'.format(len([i for i in ln]) + 3)
            elif range and ln and 101 < range <= 1000:
                # Need extra for '.' (1 extra)
                fmt = 'F{}.1'.format(len([i for i in ln]) + 2)
            else:
                # No range, must not be populated, copied from REAL4/8(s) above
                # OR we don't care because it's a 'big' number:
                fmt = 'G10.2E3'
        elif cdftype in (spacepy.pycdf.const.CDF_CHAR.value,
                         spacepy.pycdf.const.CDF_UCHAR.value):
            fmt = 'A{}'.format(v.nelems())
        else:
            raise ValueError("Couldn't find FORMAT for {} of type {}".format(
                v.name(),
                spacepy.pycdf.lib.cdftypenames.get(cdftype, 'UNKNOWN')))
        if dryrun:
            print(fmt)
        else:
            if 'FORMAT' in v.attrs:
                del v.attrs['FORMAT']
            v.attrs.new('FORMAT', data=fmt, type=spacepy.pycdf.const.CDF_CHAR)

    def nanfill(v):
        """Set fill values to NaN

        Finds all values which are equal to ``FILLVAL``, greater than
        ``VALIDMAX``, or less than ``VALIDMIN``, and replace with ``NaN``
        (not-a-number). This is an update-in-place operation; does not return
        a copy.

        Assumes a single value for ``VALIDMIN``, ``VALIDMAX``, ``FILLVAL``
        (although if the attribute is not present, will simply assume no
        restriction.)

        Only applicable to floating-point types. Best applied to a
        :class:`~spacepy.pycdf.VarCopy` or :class:`~spacepy.datamodel.dmarray`
        rather than :class:`~spacepy.pycdf.Var`. Updating a variable in a CDF
        requires one write per changed value, and also will result in a CDF
        that is no longer ISTP compliant.

        Because of floating-point comparison, the matching to ``FILLVAL`` may
        fail.

        Parameters
        ----------
        v : :class:`~spacepy.pycdf.Var` or :class:`~spacepy.datamodel.dmarray`
            CDF variable, data, or copy to update

        Examples
        --------
        >>> import spacepy.pycdf
        >>> import spacepy.pycdf.istp
        >>> f = spacepy.pycdf.CDF('foo.cdf', create=True)
        >>> v = f.new('Var', data=[1, 2, 3, -1e31])
        >>> spacepy.pycdf.istp.fillval(v)
        >>> data = v.copy()
        >>> data
        VarCopy([1., 2., 3., -1.e31], dtype=float32)
        >>> spacepy.pycdf.istp.nanfill(data)
        >>> data
        VarCopy([1., 2., 3., nan], dtype=float32)
        """
        #If input is a zVar, read all the data; if not, this is a no-copy operation
        indata = v[...]
        badidx = numpy.zeros(shape=v.shape, dtype=bool)
        if 'FILLVAL' in v.attrs:
            badidx |= (indata == v.attrs['FILLVAL'][...])
        if 'VALIDMIN' in v.attrs:
            badidx |= (indata < v.attrs['VALIDMIN'][...])
        if 'VALIDMAX' in v.attrs:
            badidx |= (indata > v.attrs['VALIDMAX'][...])
        #Try a simple assignment with fancy indexing
        try:
            v[badidx] = numpy.nan
        except (IndexError, ValueError):
            pass
        else:
            return #success
        #Fancy indexing failed, do element-by-element assignment
        badidx = numpy.transpose(badidx.nonzero())
        for i in badidx:
            v[tuple(i)] = numpy.nan

    class VarBundle(object):
        """Collective handling of ISTP-compliant variable and its dependencies.

        Representation of an ISTP-compliant variable bundled together
        with its dependencies to enable aggregate operations. Normally
        used to copy a subset of data from one CDF to another by
        chaining operations.

        Unusual or indecipherable error messages may indicate an ISTP
        compliance issue; see :class:`VariableChecks` for some checks.

        Parameters
        ----------
        var : :class:`~spacepy.pycdf.Var`
            Variable to process

        Examples
        --------
        >>> import spacepy.pycdf
        >>> import spacepy.pycdf.istp
        >>> #https://rbsp-ect.newmexicoconsortium.org/data_pub/rbspa/hope/level3/pitchangle/2012/
        >>> infile = spacepy.pycdf.CDF('rbspa_rel04_ect-hope-PA-L3_20121201_v7.1.0.cdf')
        >>> infile['FPDU']
        <Var:
        CDF_FLOAT [3228, 11, 72]
        >
        >>> infile['FPDU'].attrs
        <zAttrList:
        CATDESC: HOPE differential proton flux [CDF_CHAR]
        DEPEND_0: Epoch_Ion [CDF_CHAR]
        DEPEND_1: PITCH_ANGLE [CDF_CHAR]
        DEPEND_2: HOPE_ENERGY_Ion [CDF_CHAR]
        ...
        >
        >>> b = spacepy.pycdf.istp.VarBundle(infile['FPDU'])
        >>> outfile = spacepy.pycdf.CDF('output.cdf', create=True)
        >>> b.slice(1, 2, single=True).output(outfile)
        <VarBundle:
        FPDU: CDF_FLOAT [3228, 72]
        Epoch_Ion: CDF_EPOCH [3228]
            Epoch_Ion_DELTA: CDF_REAL4 [3228]
        PITCH_ANGLE: CDF_FLOAT ---
            Pitch_LABL: CDF_CHAR*5 ---
        HOPE_ENERGY_Ion: CDF_FLOAT [3228, 72]
            ENERGY_Ion_DELTA: CDF_FLOAT [3228, 72]
            Energy_LABL: CDF_CHAR*3 [72] NRV
        >
        >>> outfile['FPDU']
        <Var:
        CDF_FLOAT [3228, 72]
        >
        >>> outfile['FPDU'].attrs
        <zAttrList:
        CATDESC: HOPE differential proton flux [CDF_CHAR]
        DEPEND_0: Epoch_Ion [CDF_CHAR]
        DEPEND_1: HOPE_ENERGY_Ion [CDF_CHAR]
        ...
        >
        >>> outfile.close()
        >>> infile.close()

        .. autosummary::

            mean
            operations
            output
            slice
            sum
            variables

        .. automethod:: mean
        .. automethod:: output
        .. automethod:: operations
        .. automethod:: slice
        .. automethod:: sum
        .. automethod:: variables

        """

        def __init__(self, var):
            """Initialize variable bundle

            Parameters
            ----------
            var : :class:`~spacepy.pycdf.Var`
                Variable to process
            """
            self.mainvar = var
            """The variable to operate on."""
            self.cdf = self.mainvar.cdf_file
            """Input CDF file containing the main variable."""
            self._varinfo = {}
            """Keyed by variable name. Values are also dicts, keys are
            ``dims``, list of the main variable dimensions corresponding
            to each dimension of the variable, ``slice``, the slice
            to apply when reading this variable from the input, ``postidx``,
            a numpy fancy index to apply after reading, ``thisdim``,
            the main dimension for which this var is a dep
            (and thus it should be removed if the dim is removed),
            ``vartype``, whether this variable is the main var (M),
            a dependency (D), or DELTA of the main (U, for uncertainty),
            ``sortorder``, the order in which it should be displayed (0 for
            the main variable, 1 for dependencies, 2 for all DELTAs, and 3 for
            labels).
            """
            self._degenerate = []
            """Index by dim, is it degenerate, i.e. removed in a slice."""
            self._summed = []
            """Index by dim, is this dim summed."""
            self._mean = []
            """Index by dim, is this dim averaged."""
            self._getvarinfo()

        def _process_delta(self, mainvar, deltaname):
            """Handle DELTA_PLUS/DELTA_MINUS attributes

            A DELTA variable should be the same shape and the same
            dependencies as its referrer (except potentially NRV).

            Parameters
            ----------
            mainvar : :class:`~spacepy.pycdf.Var`
                Variable that references the DELTA, i.e. it has a
                DELTA_PLUS_VAR/DELTA_MINUS_VAR attribute that references
                ``deltavar``.

            deltaname : str
                Name of the DELTA variable itself.

            Returns
            -------
            dict
                dims/slice information suitable for inclusion in ``_varinfo``.
            """
            thisvar = self.cdf[deltaname]
            mainname = mainvar.name()
            for a in thisvar.attrs: #Check that all dependencies match
                if not a.startswith(('DEPEND_', 'LABL_PTR_')):
                    continue
                if a in mainvar.attrs:
                    if thisvar.attrs[a] != mainvar.attrs[a]:
                        raise ValueError('{}: attribute {} mismatch with main var'
                                         .format(deltaname, a))
                elif thisvar.attrs[a] != mainname:
                    raise ValueError('{}: attribute {} not in main var'
                                     .format(deltaname, a))
            if thisvar.rv() and not mainvar.rv():
                raise ValueError(
                    '{}: Cannot handle RV DELTA with NRV variable.'
                    .format(deltaname))
            thisshape = thisvar.shape
            mainshape = mainvar.shape
            if not thisvar.rv() and mainvar.rv(): #Ignore record dim
                mainshape = mainshape[1:]
            if thisshape != mainshape:
                raise ValueError('{}: DELTA/main var shape mismatch.'
                                 .format(deltaname))
            #If this is NRV and main is RV, that's okay, the R dim will
            #get removed when actually slicing.
            result = { k: self._varinfo[mainname][k][:]
                      for k in ('dims', 'slice', 'postidx') }
            result['sortorder'] = 2
            return result

        def _getvarinfo(self):
            """Find dependency and dimension information

            For main variable and its dependencies, find how dimensions
            relate to the main variable, and find all DELTA variables.
            """
            name = self.mainvar.name()
            #Every dim maps back to itself for the main variable
            dims = list(range(len(self.mainvar.shape)
                              + int(not self.mainvar.rv())))
            self._degenerate = [False] * len(self.mainvar.shape)
            self._summed = [False] * len(self.mainvar.shape)
            self._mean = [False] * len(self.mainvar.shape)
            if not self.mainvar.rv(): #Fake the 0-dim
                self._degenerate.insert(0, False)
                self._summed.insert(0, False)
                self._mean.insert(0, False)
            #And every dimension is a full slice, to start
            self._varinfo[name] = {
                'dims': dims,
                'slice': [slice(None)] * len(dims),
                'postidx': [slice(None)] * len(dims),
                'sortorder': 0,
                'vartype': 'M',
            }
            mainattrs = self.mainvar.attrs
            #Get the attributes that matter in the MAIN var
            attrs = {a: mainattrs[a] for a in mainattrs
                    if a.startswith(('DEPEND_', 'LABL_PTR'))
                    or a in ('DELTA_PLUS_VAR', 'DELTA_MINUS_VAR')}
            for a in attrs: #Process DEPEND/LABL_PTR variables
                if not a.startswith(('DEPEND_', 'LABL_PTR_')):
                    continue
                thisname = attrs[a]
                if thisname in self._varinfo: #Already handled
                    if self._varinfo[thisname]['sortorder'] == 3 \
                       and a.startswith('DEPEND_'):
                        #Processed before as a LABL, but also is a DEPEND.
                        #Technically ISTP violation, but have the DEPEND take
                        #priority
                        self._varinfo[thisname]['sortorder'] = 1
                    continue
                thisvar = self.cdf[thisname]
                #Dimension of main var that corresponds to this var
                dim = int(a.split('_')[-1])
                dims = [0,] #Record dim always matches
                #For every CDF (non-record) dim, match to the main variable
                for i in range(1, len(thisvar.shape) + int(not thisvar.rv())):
                    #DEPEND; LABL_PTR for this dimension
                    dim_dep = 'DEPEND_{}'.format(i)
                    labl_dep = 'LABL_PTR_{}'.format(i)
                    if not dim_dep in thisvar.attrs:
                        #No depend on this dim, so it's the dim that's represented
                        #in this variable
                        dims.append(dim)
                    else: #Match to parent var
                        dim_dep = thisvar.attrs[dim_dep]
                        parentdim = next((
                            int(d.split('_')[-1]) for d in attrs
                            if (d.startswith('DEPEND_') and attrs[d] == dim_dep)
                            or (d.startswith('LABL_PTR_') and attrs[d] == labl_dep)
                        ), None)
                        if parentdim is None:
                            raise ValueError('Cannot match dim {} of {}'.format(
                                i, thisname))
                        dims.append(parentdim)
                if dims.count(dim) != 1:
                    raise ValueError('Cannot find unique dimension for {}'
                                     .format(thisname))
                self._varinfo[thisname] = {
                    'dims': dims,
                    'slice': [slice(None)] * len(dims),
                    'postidx': [slice(None)] * len(dims),
                    'sortorder': 1 if a.startswith('DEPEND_') else 3,
                    'thisdim': dim,
                    'vartype': 'D',
                }
                #Process DELTAs of the DEPENDs
                for d in ('DELTA_PLUS_VAR', 'DELTA_MINUS_VAR'):
                    if d not in thisvar.attrs:
                        continue
                    deltaname = thisvar.attrs[d]
                    if deltaname in self._varinfo:
                        continue
                    self._varinfo[deltaname] \
                        = self._process_delta(thisvar, deltaname)
                    self._varinfo[deltaname]['vartype'] = 'D' #just like other deps
                    self._varinfo[deltaname]['thisdim'] = dim
            for a in ('DELTA_PLUS_VAR', 'DELTA_MINUS_VAR'): #Process DELTA vars
                if not a in attrs:
                    continue
                thisname = attrs[a]
                if thisname not in self._varinfo:
                    #If DELTA_PLUS/DELTA_MINUS are same var, skip second one
                    self._varinfo[thisname] \
                        = self._process_delta(self.mainvar, thisname)
                    self._varinfo[thisname]['vartype'] = 'U'

        def slice(self, dim, start=None, stop=None, step=None,
                  single=False):
            """Slice on a single dimension

            Selects subset of a dimension to include in the output. Slicing
            is done with reference to the dimensions of the main variable and
            the corresponding dimensions of all other variables are sliced
            similarly. The first non-record dimension of the variable is always
            1; 0 is the record dimension (and is ignored for NRV variables).
            Multiple slices can be applied to select subsets of multiple
            dimensions; however, if one dimension is indexed multiple
            times, only the last one in the chain takes effect.

            Interpretation of the slice parameters is like normal Python slicing,
            including the ability to use negative values, etc.

            Passing in only a dimension "resets" the slice to include the
            entire dimension.

            Parameters
            ----------
            dim : int
                CDF dimension to slice on. This is the dimension as specified
                in the CDF (0-base for RV variables, 1-base for NRV) and does
                not change with successive slicing. Each dimension can only be
                sliced once.

            single : bool
                Treat ``start`` as a single index and return only that index
                (reducing dimensionality of the data by one.)

            start : int
                Index of first element of ``dim`` to include in the output.
                This can also be a sequence of indices to include, in which
                case ``stop`` and ``step`` must not be specified. This can be
                substantially slower than specifying ``stop`` and ``step``.

            stop : int
                Index of first element of ``dim`` to exclude from the output.

            step : int
                Increment between elements to include in the output.

            Returns
            -------
            VarBundle
                This bundle, for method chaining. This is not a copy: the
                original object is updated.

            Examples
            --------
            See the :class:`VarBundle` examples for creating output from
            the slices.

            >>> import spacepy.pycdf
            >>> import spacepy.pycdf.istp
            >>> infile = spacepy.pycdf.CDF('rbspa_rel04_ect-hope-PA-L3_20121201_v7.1.0.cdf')
            >>> b = spacepy.pycdf.istp.VarBundle(infile['FPDU'])
            >>> #Select index 2 from axis 1
            >>> b.slice(1, 2, single=True)
            >>> #Select from index 5 to end for axis 2, keeping index 2 from axis 1
            >>> b.slice(2, 5)
            >>> #Select 10 through 15 on axis 2, but all of axis 1
            >>> b.slice(1).slice(2, 10, 15)
            >>> #Select just record 5 and 10
            >>> b.slice(2).slice(0, [5, 10])
            >>> infile.close()
            """
            if single and (self._summed[dim] or self._mean[dim]):
                raise ValueError('Cannot sum/average on a single-element slice.')
            self._degenerate[dim] = single

            fancyidx = (stop is None and step is None and numpy.ndim(start) != 0)
            sl = slice(None, None, None) if fancyidx else slice(start, stop, step)
            for v in self._varinfo.values():
                if not dim in v['dims']:
                    continue #This "main" var dimension isn't in this var
                idx = v['dims'].index(dim)
                #The slice to perform on read
                v['slice'][idx] = start if single else sl
                #And the slice to perform after the fact
                if fancyidx:
                    v['postidx'][idx] = start
            return self

        def sum(self, dim):
            """Sum across a dimension.

            Total the main variable of the bundle across the given dimension.
            That dimension disappears from the output and dependencies
            (including their uncertainties) are assumed to be constant across
            the summed dimension. The uncertainty of the main variable, if
            any, is appropriately propagated (quadrature sum.)

            An invalid value for any element summed over will result in a fill
            value on the output. This does not work well for variables that
            define multiple VALIDMIN/VALIDMAX based on position within a
            dimension; the smallest VALIDMIN/largest VALIDMAX rather than the
            position-specific value.

            Summing occurs after slicing, to allow summing of a subset of
            a dimension. A single element slice (which removes the dimension)
            is incompatible with summing over that dimension.

            There is not currently a way to "undo" a sum; create a new
            bundle instead.

            Parameters
            ----------
            dim : int
                CDF dimension to total. This is the dimension as specified
                in the CDF (0-base for RV variables, 1-base for NRV) and does
                not change with successive slicing or summing. This must be a
                positive number (no support for e.g. -1 for last dimension.)

            Returns
            -------
            VarBundle
                This bundle, for method chaining. This is not a copy: the
                original object is updated.

            Examples
            --------
            See the :class:`VarBundle` examples for creating output.

            >>> import spacepy.pycdf
            >>> import spacepy.pycdf.istp
            >>> infile = spacepy.pycdf.CDF('rbspa_rel04_ect-hope-PA-L3_20121201_v7.1.0.cdf')
            >>> b = spacepy.pycdf.istp.VarBundle(infile['Counts_P'])
            >>> #Total over dimension 1 (pitch angle)
            >>> b.sum(1)
            >>> #Get a new bundle (without the previous sum)
            >>> b = spacepy.pycdf.istp.VarBundle(infile['Counts_P'])
            >>> #Total over first 10 elements of dimension 2 (energy bins)
            >>> b.slice(2, 0, 10).sum(2)
            >>> infile.close()
            """
            if self._degenerate[dim]:
                raise ValueError('Cannot sum on a single-element slice.')
            if self._mean[dim]:
                raise ValueError('Cannot sum and take mean of same dimension.')
            self._summed[dim] = True
            return self

        def mean(self, dim):
            """Take the mean of a dimension.

            Take mean of the main variable of the bundle across the given
            dimension. That dimension disappears from the output and dependencies
            (including their uncertainties) are assumed to be constant across
            the summed dimension. The uncertainty of the main variable, if
            any, is appropriately propagated.

            Invalid values are excluded fromthe mean. This does not work well
            for variables that define multiple VALIDMIN/VALIDMAX based on
            position within a dimension; the smallest VALIDMIN/largest VALIDMAX
            rather than the position-specific value.

            Averaging occurs after slicing, to allow averaging of a subset of
            a dimension. A single element slice (which removes the dimension)
            is incompatible with averaging over that dimension.

            There is not currently a way to "undo" a mean; create a new
            bundle instead.

            Parameters
            ----------
            dim : int
                CDF dimension to average. This is the dimension as specified
                in the CDF (0-base for RV variables, 1-base for NRV) and does
                not change with successive slicing or summing. This must be a
                positive number (no support for e.g. -1 for last dimension.)

            Returns
            -------
            VarBundle
                This bundle, for method chaining. This is not a copy: the
                original object is updated.

            Examples
            --------
            See the :class:`VarBundle` examples for creating output.

            >>> import spacepy.pycdf
            >>> import spacepy.pycdf.istp
            >>> infile = spacepy.pycdf.CDF('rbspa_rel04_ect-hope-PA-L3_20121201_v7.1.0.cdf')
            >>> b = spacepy.pycdf.istp.VarBundle(infile['Counts_P'])
            >>> #Average over dimension 1 (pitch angle)
            >>> b.mean(1)
            >>> #Get a new bundle (without the previous sum)
            >>> b = spacepy.pycdf.istp.VarBundle(infile['Counts_P'])
            >>> #Average over first 10 elements of dimension 2 (energy bins)
            >>> b.slice(2, 0, 10).mean(2)
            >>> infile.close()
            """
            if self._degenerate[dim]:
                raise ValueError('Cannot average on a single-element slice.')
            if self._summed[dim]:
                raise ValueError('Cannot sum and take mean of same dimension.')
            self._mean[dim] = True
            return self

        def _tokeep(self):
            """Determine which variables to keep for output

            Dependencies for dimensions which disappear after slicing, and
            other variables that they depend on, shouldn't be included in
            the output

            Returns
            -------
            list of str
                Names of variables to include in the output.
            """
            #What dims of main var disappear?
            deleted = [i for i in range(len(self._degenerate))
                       if any((self._degenerate[i], self._summed[i],
                               self._mean[i]))]
            return [v for v, i in self._varinfo.items()
                    if i.get('thisdim', None) not in deleted]

        def _same(self, newvar, invar, rv, dv, dims, data):
            """Checks if an existing variable matches a proposed new variable

            Does not compare DEPEND and LABL_PTR attributes (those are handled
            later.)

            Parameters
            ----------
            newvar : :class:`~spacepy.pycdf.Var`
                Existing variable to compare to requirements

            invar : : class:`~spacepy.pycdf.Var`
                Variable to use as reference for attributes, RV, CDF type,
                number of elements.

            rv : bool
                Is the new variable record-varying

            dv : list of bool
                Data variance for each dimension.

            dims : list of int
                Size of each dimension.

            data : :class:`~numpy.ndarray`
                Data that should be in the variable.

            Returns
            -------
            bool
                True if the existing variable is the same; False if not.
            """
            #Check basic type, dimensions, etc.
            if newvar.rv() != rv or newvar.type() != invar.type() \
                or len(dims) != (len(newvar.shape) - newvar.rv()) \
                or newvar.dv() != dv or newvar.nelems() != invar.nelems() \
                or list(dims) != list(newvar.shape[newvar.rv():]):
                return False
            ia = invar.attrs
            na = newvar.attrs
            for a in ia:
                if a.startswith(('DEPEND_', 'LABL_PTR_')) \
                   or a == 'FIELDNAM':
                    #depends/LABL PTR shift around, and FIELDNAM may change,
                    #so test outside of this function.
                    pass
                if not a in na or ia.type(a) != na.type(a) \
                   or not numpy.array_equal(ia[a], na[a]):
                    return False
            #Finally check the data
            return (data == newvar[...]).all()

        def _namemap(self, suffix=None):
            """Map old variable names to new

            Helper for :meth:`output` that maps the variable name in the
            input CDF to variable name in the output CDF.

            Parameters
            ----------
            suffix : str
                String to append to name of variables that are changed
                from input to output.

            Returns
            -------
            dict
                Keyed by name in input, values are name in the output. No
                entry for names that don't change.
            """
            namemap = {}
            if suffix is not None:
                for vname, vinfo in self._varinfo.items():
                    if vinfo['vartype'] in ('M', 'U'):
                        namemap[vname] = vname + suffix
                    else: #Dependency. If any slice/sum, it's changed
                        if any([any((self._summed[d], self._mean[d]))
                                for d in vinfo['dims']]) \
                        or any([s != slice(None) for s in itertools.chain(
                            vinfo['slice'], vinfo['postidx'])]):
                            namemap[vname] = vname + suffix
            return namemap

        def _sum_avg(self, data, invar, vinfo, degen, summed, averaged):
            """Sum/average data

            Helper for :meth:`output` that performs summing and averaging
            of the data for a single variable. Note dimensionality of all
            input is before the removal of degenerate dimensions
            (this function does the translation using ``degen``), and it is
            by dimension not axis (so NRV variables have a vestigial 0th
            dimension that is not interpreted.)

            Parameters
            ----------
            data : :class:`numpy.ndarray`
                Data as read from input CDF and properly sliced.

            invar : :class:`~spacepy.pycdf.Var`
                CDF input variable from which ``data`` was read.

            vinfo : dict
                Value from instance variable ``_varinfo`` for this variable.

            degen : list of bool
                For each dimension of this variable, whether the dimension
                is degenerate (i.e. already gone at this point.)

            summed : list of bool
                For each dimension of this variable, whether the dimension
                should be summed over.

            averaged : list of bool
                For each dimension of this variable, whether the dimension
                should be averaged over.

            Returns
            -------
            :class:`numpy.ndarray`
                Data summed/averaged over dimensions according to ``summed``
                and ``averaged`` inputs.
            """
            #Correction for NRV variables in the mapping between dim and axis
            nrv = int(not invar.rv())
            #Degenerate slices have already been removed, so need
            #a map from old dim numbers to new ones. Note removing
            #the record dimension does not shift other dims!
            newdims = [None if degen[i] else i - sum(degen[1:i])
                       for i in range(len(degen))]
            #Axis numbers to sum, with degenerate removed
            #(NRV means dim 0 is axis 1, so correct for that,
            #and also don't do any actions on dim 0 for NRV)
            summe = [newdims[i] - nrv
                     for i in range(nrv, len(summed)) #old dim
                     if newdims[i] is not None and (summed[i] or averaged[i])]
            avgme = [newdims[i] - nrv
                     for i in range(nrv, len(averaged)) #old dim
                     if newdims[i] is not None and averaged[i]]
            #Sum over axes in reverse order so axis renumbering
            #doesn't affect future sums
            a = invar.attrs
            for ax in summe[::-1]:
                if vinfo['vartype'] == 'D':
                    #If sum over DEPEND, must be constant over axis
                    data = data.take(0, axis=ax)
                    continue
                invalid = numpy.isclose(data, a['FILLVAL'])
                if 'VALIDMIN' in a:
                    invalid = numpy.logical_or(
                        invalid, data < numpy.min(a['VALIDMIN']))
                if 'VALIDMAX' in a:
                    invalid = numpy.logical_or(
                        invalid, data > numpy.max(a['VALIDMAX']))
                data[invalid] = 0 #avoids warning and helps with mean
                if vinfo['vartype'] == 'M':
                    data = data.sum(axis=ax)
                elif vinfo['vartype'] == 'U': #propagate error
                    data = numpy.sqrt((data ** 2).sum(axis=ax))
                else: #Should not happen
                    raise ValueError('Bad summation type.')
                if ax in avgme: #divide out
                    count = numpy.sum(~invalid, axis=ax)
                    invalid = (count == 0)
                    count[invalid] = 1 #avoid warning
                    data = data / count
                else: #Sum, so any fill on axis means value is fill
                    invalid = invalid.max(axis=ax)
                data[invalid] = a['FILLVAL']
            return data

        def _repoint_depend(self, invar, newvar, preexist, namemap, degen):
            """Change DEPEND for new dimensionality of one variable.

            Slicing/summing might change variable dimensionality and thus
            the relationship with its DEPENDs, and the DEPENDs themselves
            may have a new name. This updates the DEPEND attributes for
            these changes, or verifies they are correct if the output
            variable already exists.

            Parameters
            ----------
            invar : :class:`~spacepy.pycdf.Var`
                The input variable (opened in raw mode).

            newvar : :class:`~spacepy.pycdf.Var`
                The output variable (opened in raw mode).

            preexist : bool
                True if ``newvar`` existed and doing a consistency check;
                False if ``newvar`` was newly created and should be edited.

            namemap : dict
                Map from name in input variable (key) to name in output
                variable (value). No entry if name didn't change.

            degen : list of bool
                For each dimension of this variable, whether the dimension
                is degenerate (i.e. already gone at this point.) This
                includes any degeneracy from summing/averaging as well as
                slicing.

            """
            #Index by old dim; returns the new dim (None if went away)
            #Note slicing away DEPEND_0 (record dimension) does NOT change
            #subsequent depends!
            newdims = [None if degen[i] else i - sum(degen[1:i])
                       for i in range(len(degen))]
            for a in list(newvar.attrs.keys()): #Editing in loop!
                #Handle a suffixed DELTA if necessary
                if a.startswith('DELTA_'):
                    olddelta = invar.attrs[a]
                    if str is not bytes and isinstance(olddelta, bytes):
                        olddelta = olddelta.decode('ascii')
                    newvar.attrs[a] = namemap.get(olddelta, olddelta)
                    continue
                if not a.startswith(('DEPEND_', 'LABL_PTR_')):
                    continue
                newdim = int(a.split('_')[-1])
                oldval = None #Sentinel value
                if newdim in newdims: #An old value that belongs in this dim
                    olddim = newdims.index(newdim)
                    old_a = '{}_{}'.format('_'.join(a.split('_')[:-1]),
                                           olddim)
                    oldval = invar.attrs.get(old_a, None)
                    if str is not bytes and isinstance(oldval, bytes):
                        oldval = oldval.decode('ascii')
                if oldval is not None:
                    #Check for variable renaming from the input to output
                    newval = namemap.get(oldval, oldval)
                    if preexist:
                        existingval = newvar.attrs[a]
                        if str is not bytes and isinstance(existingval, bytes):
                            existingval = existingval.decode('ascii')
                        if existingval != newval:
                            raise RuntimeError(
                                'Incompatible {} already exists in output.'
                                .format(newvar.name()))
                    else:
                        newvar.attrs[a] = newval
                else:
                    #Either there's no corresponding old dim, or it didn't have
                    #a DEPEND. Either way, shouldn't be a DEPEND in the new dim.
                    if preexist:
                        if a in newvar.attrs:
                            raise RuntimeError(
                                'Incompatible {} already exists in output.'
                                .format(newvar.name()))
                    else:
                        del newvar.attrs[a]

        def _outshape(self, vname):
            """Calculate shape of the variable on output

            Parameters
            ----------
            vname : str
                Name of the variable to check the shape of.

            Returns
            -------
            tuple
                The shape of the variable after all slicing, etc. applied, or
                None of the variable is not included in output.
            """
            if vname not in self._tokeep():
                return None
            vinfo = self._varinfo[vname]
            invar = self.cdf[vname]
            rv = invar.rv()
            shape = invar.shape
            sl = vinfo['slice']
            postidx = vinfo['postidx']
            #no dimension has BOTH a slice and a postindex, so combine
            slices = [pi if s == slice(None, None, None) else s
                      for s, pi in zip(sl, postidx)]
            #And any dim that is summed/averaged is degenerate, so
            #slice with a single index to make it go away
            for d in vinfo['dims']:
                if self._summed[d] or self._mean[d]:
                    slices[d] = 0
            if not rv: #Remove record dimension
                slices = slices[1:]
            #Make a fake array the size of the input, and slice it
            return numpy.empty(shape=shape)[tuple(slices)].shape

        def variables(self):
            """Description of variable output from the bundle

            Provides information describing the variables output
            from the bundle

            Returns
            -------
            list
                Each element is a list-of-tuples. The list corresponds to a
                dimension of the master var: first the master var itself, then the
                uncertainties and labels associated with each dimension. Each
                element of these sublists is then a tuple of variable name and
                shape on the output (itself a tuple). If a variable isn't
                included in the output (sliced away), its shape will be ``None``.

            Examples
            --------
            >>> import spacepy.pycdf
            >>> import spacepy.pycdf.istp
            >>> infile = spacepy.pycdf.CDF('rbspa_rel04_ect-hope-PA-L3_20121201_v7.1.0.cdf')
            >>> b = spacepy.pycdf.istp.VarBundle(infile['FPDU'])
            >>> b.slice(1, 2, single=True).variables()
            [[('FPDU', (100, 72))],
             [('Epoch_Ion', (100,)), ('Epoch_Ion_DELTA', (100,))],
             [('PITCH_ANGLE', None), ('Pitch_LABL', None)],
             [('HOPE_ENERGY_Ion', (100, 72)),
              ('ENERGY_Ion_DELTA', (100, 72)),
              ('Energy_LABL', (72,))]]
            """
            #List of every variable in each dimension
            v_by_dim = functools.reduce(
                lambda x, vname:
                x[self._varinfo[vname].get('thisdim', None)].append(vname) or x,
                self._varinfo.keys(), collections.defaultdict(list))
            for l in v_by_dim.values():
                l.sort(key=lambda x: (self._varinfo[x]['sortorder'], x))
            variables = [[(v, self._outshape(v))
                          for v in v_by_dim.get(None, [])]]
            vi = self._varinfo[self.mainvar.name()]
            for dim in vi['dims']:
                variables.append([
                    (v, self._outshape(v)) for v in v_by_dim.get(dim, [])])
            return variables

        def operations(self):
            """Operations of this bundle

            Provides information describing the operations this bundle
            would perform.

            Returns
            -------
            list
                Each element is a tuple: first element is a string with
                the name of the operation (i.e. method of
                :class:`VarBundle`), next is also a tuple of positional
                arguments, and finally a dict of keyword arguments.

            Examples
            --------
            >>> import spacepy.pycdf
            >>> import spacepy.pycdf.istp
            >>> infile = spacepy.pycdf.CDF('rbspa_rel04_ect-hope-PA-L3_20121201_v7.1.0.cdf')
            >>> b = spacepy.pycdf.istp.VarBundle(infile['FPDU'])
            >>> b.slice(1, 2, single=True).operations()
              [('slice', (1, 2), {'single': True})]
            >>> #Apply same operations to a different variable
            >>> b2 = spacepy.pycdf.istp.VarBundle(infile['FEDU'])
            >>> for op, args, kwargs in b2.operations():
            ...     getattr(b2, op)(*args, **kwargs)
            """
            ops = []
            vi = self._varinfo[self.mainvar.name()]
            for dim in vi['dims']:
                sl = vi['slice'][dim]
                postidx = vi['postidx'][dim]
                if sl != slice(None, None, None): #simple slice
                    if isinstance(sl, slice): #slice
                        ops.append((
                            'slice',
                            tuple((s for s in (dim, sl.start, sl.stop, sl.step)
                                   if s is not None)),
                            {}))
                    else: #single index
                        ops.append(('slice', (dim, sl), {'single': True}))
                elif postidx != slice(None, None, None): #fancy index
                    ops.append(('slice', (dim, postidx,), {}))
                for v, name in zip((self._mean, self._summed), ('mean', 'sum')):
                    if v[dim]:
                        ops.append((name, (dim,), {}))
            return ops

        def output(self, output, suffix=None):
            """Output the variables as modified

            Parameters
            ----------
            output : :class:`~spacepy.pycdf.CDF`
                Output CDF to receive the new data.

            suffix : str
                Suffix to append to the name of any variables that are changed
                for the output. This allows the output to contain multiple
                variables derived from the same input variable. The main variable
                and its DELTA variables will always have the suffix applied.
                Any dependencies will have the suffix applied only if they have
                changed from the input CDF (e.g. from slicing.)

            Returns
            -------
            VarBundle
                This bundle, for method chaining.

            Examples
            --------
            >>> import spacepy.pycdf
            >>> import spacepy.pycdf.istp
            >>> infile = spacepy.pycdf.CDF('rbspa_rel04_ect-hope-PA-L3_20121201_v7.1.0.cdf')
            >>> b = spacepy.pycdf.istp.VarBundle(infile['FPDU'])
            >>> outfile = spacepy.pycdf.CDF('output.cdf', create=True)
            >>> #Output the low energy half in one variable
            >>> b.slice(2, 0, 36).output(outfile, suffix='_LoE')
            >>> #And the high energy half in another variable
            >>> b.slice(2, 36, 72).output(outfile, suffix='_HiE')
            >>> outfile.close()
            >>> infile.close()
            """
            tokeep = self._tokeep()
            namemap = self._namemap(suffix)
            for vname in tokeep:
                vinfo = self._varinfo[vname]
                #Dim of main var that depends on this (None if main var or delta)
                maindim = vinfo.get('thisdim', None)
                #Degeneracy of dimensions in this variable's "frame"
                degen = [self._degenerate[d] for d in vinfo['dims']]
                #And whether the dim was summed
                summed = [self._summed[d] for d in vinfo['dims']]
                #And averaged
                averaged = [self._mean[d] for d in vinfo['dims']]
                invar = self.cdf.raw_var(vname)
                sl = vinfo['slice'] #including 0th dim
                postidx = vinfo['postidx']
                #Dimension size/variance for original variable
                #(0 index is CDF dimension 1)
                dv = invar.dv()
                rv = invar.rv() #and record variance
                #Scrub degenerate dimensions from the post-indexing
                #(record is never degenerate)
                postidx = [postidx[i] for i in range(len(postidx))
                           if not degen[i]]

                #Now get the data, and sum/average it
                if not rv: #Remove fake record dimension
                    sl = sl[1:]
                    postidx = postidx[1:]
                #Forces array scalars, makes the rest work better
                data = numpy.asanyarray(invar.__getitem__(tuple(sl)))
                if postidx:
                    data = data[tuple(postidx)]
                data = self._sum_avg(data, invar, vinfo, degen, summed, averaged)
                #Summed/averaged dimensions are now also degenerate
                degen = [max(v) for v in zip(degen, summed, averaged)]

                #Get shape of output variable from actual data
                dims = data.shape
                #Raw Epoch16 have a trailing (2,)
                if invar.type() == spacepy.pycdf.const.CDF_EPOCH16.value:
                    dims = dims[:-1]
                #Cut out any degenerate dimensions from DV (skipping record dim)
                dv = [dv[i] for i in range(len(dv)) if not degen[i + 1]]
                #Change record variance for the output if sliced away 0th
                if rv and degen[0]:
                    rv = False
                if rv: #remove record dimension from size IF output is RV
                    dims = dims[1:]

                #Rename the variable if necessary
                outname = namemap.get(vname, vname)
                if outname in output:
                    preexist = True
                    newvar = output.raw_var(outname)
                    if not self._same(newvar, invar, rv, dv, dims, data):
                        raise RuntimeError(
                            'Incompatible {} already exists in output.'
                            .format(outname))
                else:
                    preexist = False
                    newvar = output.new(
                        outname, type=invar.type(), recVary=rv,
                        dimVarys=dv, dims=dims,
                        n_elements=invar.nelems())
                    newvar = output.raw_var(outname)
                    #Must create it empty so can change compression
                    newvar.compress(*invar.compress())
                    newvar[...] = data
                    newvar.attrs.clone(invar.attrs)
                    if vname != outname: #renamed
                        newvar.attrs['FIELDNAM'] = outname

                self._repoint_depend(invar, newvar, preexist, namemap, degen)
            return self

        def __str__(self):
            """String representation of the bundle

            Returns a string representation of the bundle, which is all the
            variables that are involved on the input. Variables which are
            not included on the output are in []

            Returns
            -------
            str
                Brief string description of the bundle.
            """
            return '\n'.join([
                '{}{}: {} {}{}'.format(
                    ' ' * 4 if self._varinfo[vname]['sortorder'] > 1 else '',
                    vname,
                    str(self.cdf[vname]).split(' ')[0], #Grab type from Var str
                    str(list(shape)) if shape is not None else '---',
                    #RV vars always have dim 0 as axis 0, so they become
                    #NRV iff dim 0 of the main var goes away
                    ' NRV' if shape is not None
                    and (not self.cdf[vname].rv() or max(
                        self._degenerate[0], self._summed[0], self._mean[0]))
                    else ''
                )
                for dimvars in self.variables() for vname, shape in dimvars])

        def __repr__(self):
            """Representation of bundle

            Cannot return anything that can be evaluated to create a copy
            of the CDF, so this is just the informal str representation in
            angle brackets.

            Returns
            -------
            str
                Informal representation of bundle contents.
            """
            return '<VarBundle:\n{}\n>'.format(str(self))