Metadata-Version: 1.1
Name: icontract
Version: 1.2.0
Summary: Provide design-by-contract with informative violation messages
Home-page: https://github.com/Parquery/icontract
Author: Marko Ristin
Author-email: marko@parquery.com
License: UNKNOWN
Description: icontract
        =========
        
        icontract provides `design-by-contract <https://en.wikipedia.org/wiki/Design_by_contract>`_ to Python3 with informative
        violation messages.
        
        There exist a couple of contract libraries. However, at the time of this writing (July 2018), they all required the
        programmer either to learn a new syntax (`PyContracts <https://pypi.org/project/PyContracts/>`_) or to write
        redundant condition descriptions (
        *e.g.*,
        `contracts <https://pypi.org/project/contracts/>`_,
        `covenant <https://github.com/kisielk/covenant>`_,
        `dpcontracts <https://pypi.org/project/dpcontracts/>`_,
        `pyadbc <https://pypi.org/project/pyadbc/>`_ and
        `pcd <https://pypi.org/project/pcd>`_).
        
        This library was strongly inspired by them, but we go a step further and use the
        `meta <https://github.com/srossross/Meta>`_ programming library to infer violation messages from the code in order to
        promote dont-repeat-yourself principle (`DRY <https://en.wikipedia.org/wiki/Don%27t_repeat_yourself>`_) and spare the
        programmer the tedious task of repeating the message that was already written in code.
        
        We want this library to be used mainly in production code and let us spot both development and production bugs with
        enough information. Therefore, we decided to implement only the pre-conditions and post-conditions which require
        little overhead, and intentionally left out the class invariants.  Class invariants seem to us tricky to grasp (
        for example, depending on the design class invariants may hold only at the first call of the public function, but
        not in the private functions; or they may hold only at the first call to a method of a class, but not in the sequent
        calls to other class methods *etc.*). The invariants hence need to come with an overhead which is generally impractical
        for production systems.
        
        Usage
        =====
        icontract provides two decorators, ``pre`` and ``post`` for pre-conditions and post-conditions, respectively.
        
        The ``condition`` argument specifies the contract and is usually written in lambda notation. In post-conditions,
        condition function receives a reserved parameter ``result`` corresponding to the result of the function. The condition
        can take as input a subset of arguments required by the wrapped function. This allows for very succinct conditions.
        
        You can provide an optional description by passing in ``description`` argument.
        
        Whenever a violation occurs, ``ViolationError`` is raised. Its message includes:
        
        * the human-readable representation of the condition,
        * description (if supplied) and
        * representation of all the values.
        
        You can provide a custom representation function with the argument ``repr_args`` that needs to cover all the input
        arguments (including ``result`` in post-conditions) of the condition function and return a string. If no representation
        function was specified, the input arguments are represented by concatenation of ``__repr__`` on each one of them.
        
        If no custom representation function has been supplied, the representation of the values is obtained by re-executing
        the condition function programmatically by traversing its abstract syntax tree and filling the tree leaves with
        values held in the function frame. Mind that this re-execution will also re-execute all the functions.
        Therefore you need to make sure that all the function calls involved in the condition functions do not have any side
        effects.
        
        .. code-block:: python
        
            >>> import icontract
        
            >>> @icontract.pre(lambda x: x > 3)
            ... def some_func(x: int, y: int = 5)->None:
            ...     pass
            ...
        
            >>> some_func(x=5)
        
            # Pre-condition violation
            >>> some_func(x=1)
            Traceback (most recent call last):
              ...
            icontract.ViolationError: Precondition violated: x > 3: x was 1
        
            # Pre-condition violation with a description
            >>> @icontract.pre(lambda x: x > 3, "x must not be small")
            ... def some_func(x: int, y: int = 5) -> None:
            ...     pass
            ...
            >>> some_func(x=1)
            Traceback (most recent call last):
              ...
            icontract.ViolationError: Precondition violated: x must not be small: x > 3: x was 1
        
            # Pre-condition violation with a custom representation function
            >>> @icontract.pre(lambda x: x > 3, repr_args=lambda x: "x was {:03}".format(x))
            ... def some_func(x: int, y: int = 5) -> None:
            ...     pass
            ...
            >>> some_func(x=1)
            Traceback (most recent call last):
              ...
            icontract.ViolationError: Precondition violated: x > 3: x was 001
        
        
            # Pre-condition violation with more complex values
            >>> class B:
            ...     def __init__(self) -> None:
            ...         self.x = 7
            ...
            ...     def y(self) -> int:
            ...         return 2
            ...
            ...     def __repr__(self) -> str:
            ...         return "instance of B"
            ...
            >>> class A:
            ...     def __init__(self)->None:
            ...         self.b = B()
            ...
            ...     def __repr__(self) -> str:
            ...         return "instance of A"
            ...
            >>> SOME_GLOBAL_VAR = 13
            >>> @icontract.pre(lambda a: a.b.x + a.b.y() > SOME_GLOBAL_VAR)
            ... def some_func(a: A) -> None:
            ...     pass
            ...
            >>> an_a = A()
            >>> some_func(an_a)
            Traceback (most recent call last):
              ...
            icontract.ViolationError: Precondition violated: (a.b.x + a.b.y()) > SOME_GLOBAL_VAR:
            SOME_GLOBAL_VAR was 13
            a was instance of A
            a.b was instance of B
            a.b.x was 7
            a.b.y() was 2
        
            # Post-condition
            >>> @icontract.post(lambda result, x: result > x)
            ... def some_func(x: int, y: int = 5) -> int:
            ...     return x - y
            ...
            >>> some_func(x=10)
            Traceback (most recent call last):
              ...
            icontract.ViolationError: Post-condition violated: result > x:
            result was 5
            x was 10
        
        Installation
        ============
        
        * Install icontract with pip:
        
        .. code-block:: bash
        
            pip3 install icontract
        
        Development
        ===========
        
        * Check out the repository.
        
        * In the repository root, create the virtual environment:
        
        .. code-block:: bash
        
            python3 -m venv venv3
        
        * Activate the virtual environment:
        
        .. code-block:: bash
        
            source venv3/bin/activate
        
        * Install the development dependencies:
        
        .. code-block:: bash
        
            pip3 install -e .[dev]
        
        * We use tox for testing and packaging the distribution. Run:
        
        .. code-block:: bash
        
            tox
        
        * We also provide a set of pre-commit checks that lint and check code for formatting. Run them locally from an activated
          virtual environment with development dependencies:
        
        .. code-block:: bash
        
            ./precommit.py
        
        * The pre-commit script can also automatically format the code:
        
        .. code-block:: bash
        
            ./precommit.py  --overwrite
        
        Versioning
        ==========
        We follow `Semantic Versioning <http://semver.org/spec/v1.0.0.html>`_. The version X.Y.Z indicates:
        
        * X is the major version (backward-incompatible),
        * Y is the minor version (backward-compatible), and
        * Z is the patch version (backward-compatible bug fix).
        
Keywords: design-by-contract precondition postcondition validation
Platform: UNKNOWN
Classifier: Development Status :: 5 - Production/Stable
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: MIT License
Classifier: Programming Language :: Python :: 3.5
