
class DontHashThis(Exception):
	"""If your trimmer funcion raises this exception, then the input
			to nice_hash.add() will be ignored."""

	def __init__(self):
		Exception.__init__(self)


class NotInHash(KeyError):
	def __init__(self, s):
		KeyError.__init__(self, s)


class nice_hash(object):
	__doc__ = """This class generates a map from list items to integers,
		where an equivalence class is defined by the trimmer function."""

	def __init__(self, trimmer=None):
		"""Trimmer defines equivalence classes on list;
		it can be some sort of projection operation.
		The default (None) makes the identity class equal to the inputs.
		It can also specify which inputs to ignore."""
		self.trimmed_seen = {}
		self.seen = []
		self.n = 0
		if trimmer is None:
			def trimmer(x):
				return x
		self.trimmer = trimmer


	def add(self, x):
		"""Returns an integer which is shared among all x in the
		equivalence class, but different from all other x.
		If the trimmer function raises the DontHashThis exception,
		it will ignore the input and return None.
		Note that if you add an item twice, it will appear twice in rmap().
		@returns: int
		"""

		try:
			xt = self.trimmer(x)
		except DontHashThis:
			return None
		self.seen.append((x, xt))

		try:
			i = self.trimmed_seen[xt]
		except KeyError:
			i = self.n
			self.trimmed_seen[xt] = i
			self.n += 1
		return i


	def add_newonly(self, x):
		"""Similar to add, except it returns None if the equivalence
		class has already appeared.   The list of classes seen (self.seen) then
		contains only the first item that was added in each class,
		so L{rmap}() will produce a dictionary containing single-item lists:
		C{{int1:[item1],int2:[item2],int3:[item3], ...}}.
		Calls to L{add}() and L{add_newonly}() can be intermixed safely,
		though the result of L{rmap}() will then not contain all added items.
		@returns: int or None
		"""

		try:
			xt = self.trimmer(x)
		except DontHashThis:
			return None

		if xt in self.trimmed_seen:
			return None

		self.seen.append((x, xt))
		i = self.n
		self.trimmed_seen[xt] = i
		self.n += 1
		return i
		

	def get_image(self, x):
		"""Returns an integer which is shared among all x in the
		equivalence class, but different from all other x.
		"""

		try:
			xt = self.trimmer(x)
		except DontHashThis:
			raise NotInHash('Trimmer raised DontHashThis')
		try:
			i = self.trimmed_seen[xt]
		except KeyError:
			raise NotInHash('Key: %s' % str(xt))
		return i


	def map(self):
		"""Return the map from inputs to integers."""
		o = {}
		for (x, xt) in self.seen:
			o[x] = self.trimmed_seen[xt]
		return o


	def classes(self):
		"""Return a list over all the classes that have been seen."""
		return self.trimmed_seen.keys()


	def classmap(self):
		"""Return the map from integers to classes."""
		# o = [ None for i in range(len(self.trimmed_seen)) ]
		o = [None for q in self.trimmed_seen.keys() ]
		for (x, i) in self.trimmed_seen.iteritems():
			o[i] = x
		return  o


	def rmap(self):
		"""Returns the map from integers to inputs."""
		# o = [ [] for i in range(len(self.trimmed_seen)) ]
		o = [ [] for q in self.trimmed_seen.keys() ]
		for (x, cl) in self.seen:
			o[self.trimmed_seen[cl]].append(x)
		return o


	def test(self):
		map = self.map()
		rmap = self.rmap()
		for (intg, inpt) in rmap.iteritems():
			for s in inpt:
				assert map[s] == intg


class simple(object):
	__doc__ = """This class generates a map from inputs to integers,
		where an equivalence class is defined by the trimmer function."""



	def __init__(self, trimmer):
		"""Trimmer defines equivalence classes on list.
		It can also specify which inputs to ignore."""
		self.trimmed_seen = {}
		self.n = 0
		self.trimmer = trimmer


	def add(self, x):
		"""Returns an integer which is shared among all x in the
		equivalence class, but different from all other x.
		If the trimmer function raises the DontHashThis exception,
		it will ignore the input and return None.
		"""

		try:
			xt = self.trimmer(x)
		except DontHashThis:
			return None

		try:
			i = self.trimmed_seen[xt]
		except KeyError:
			i = self.n
			self.trimmed_seen[xt] = i
			self.n += 1
		return i
		

	def add_newonly(self, x):
		"""Same as add, except it returns None if the equivalence
		class has already appeared.
		"""

		try:
			xt = self.trimmer(x)
		except DontHashThis:
			return None

		if xt in self.trimmed_seen:
			return None

		i = self.n
		self.trimmed_seen[xt] = i
		self.n += 1
		return i
		


	def map(self):
		"""Return the map from classes (as returned by the function)
		to integers."""
		return self.trimmed_seen.copy()


	def classmap(self):
		"""Return the map from integers to classes."""
		o = {}
		for (x, i) in self.trimmed_seen.iteritems():
			o[i] = x
		return  o



def map(list, trimmer=lambda x:x):
	h = simple(trimmer)
	for x in list:
		h.add(x)
	return h.map()



if __name__ == '__main___':
	h = nice_hash(lambda x : x)
	assert h.add('foo') == 0
	assert h.add('bar') == 1
	assert h.add('gleep') == 2
	assert h.add('bar') == 1
	h.test()
	assert h.map()['bar'] == 1
	assert h.rmap()[0] == ['foo']
	assert h.classmap()[1] == 'bar'
