Metadata-Version: 1.1
Name: patchy
Version: 1.1.0
Summary: Patch the source of python functions at runtime.
Home-page: https://github.com/adamchainz/patchy
Author: Adam Johnson
Author-email: me@adamj.eu
License: BSD
Description: ======
        Patchy
        ======
        
        .. image:: https://img.shields.io/travis/adamchainz/patchy.svg
                :target: https://travis-ci.org/adamchainz/patchy
        
        .. image:: https://img.shields.io/pypi/v/patchy.svg
                :target: https://pypi.python.org/pypi/patchy
        
        .. figure:: https://raw.github.com/adamchainz/patchy/master/pirate.png
           :alt: A patchy pirate.
        
        ..
        
        Patch the source of python functions at runtime.
        
        A quick example:
        
        .. code-block:: python
        
            >>> def sample():
            ...    return 1
            >>> patchy.patch(sample, """\
            ...     @@ -1,2 +1,2 @@
            ...      def sample():
            ...     -    return 1
            ...     +    return 9001
            ...     """)
            >>> sample()
            9001
        
        
        Why?
        ====
        
        If you’re monkey-patching an external library to add or fix some functionality,
        you will probably forget to check the monkey patch when you upgrade it. By
        using a patch against its source code, you can specify some context that you
        expect to remain the same in the function that will be checked before the
        source is applied.
        
        I found this with some small but important patches to Django for a project.
        Since it takes a lot of energy to maintain a fork, writing monkey patches was
        the chosen quick solution, but then writing actual patches would be better.
        
        The patches are applied with the standard ``patch`` commandline utility.
        
        
        Why not?
        ========
        
        There are of course a lot of reasons against:
        
        * It’s (relatively) slow (since it writes the source to disk and calls the
          ``patch`` command)
        * If you have a patch file, why not just fork the library and apply it?
        * At least with monkey-patching you know you end up with, rather than having a
          the changes being done at runtime
        
        All are valid arguments. However once in a while this might be the right
        solution.
        
        
        How?
        ====
        
        The standard library function ``inspect.getsource()`` is used to retrieve the
        source code of the function, the patch is applied with the commandline utility
        ``patch``, the code is recompiled, and the function’s code object is replaced
        the new one. Because nothing tends to poke around at code objects apart from
        dodgy hacks like this, you don’t need to worry about chasing any references
        that may exist to the function, unlike ``mock.patch``.
        
        
        API
        ===
        
        ``patch(func, patch_text)``
        ---------------------------
        
        Apply the patch ``patch_text`` to the source of function ``func``.
        
        If the patch is invalid, for example the context lines don’t match,
        ``ValueError`` will be raised, with a message that includes all the output from
        the ``patch`` utility.
        
        Note that ``patch_text`` will be ``textwrap.dedent()``’ed, but leading
        whitespace will not be removed. Therefore the correct way to include the patch
        is with a triple-quoted string with a backslash - ``"""\`` - which starts the
        string and avoids including the first newline. A final newline is not required
        and will be automatically added if not present.
        
        Example:
        
        .. code-block:: python
        
            import patchy
        
            def sample():
                return 1
        
            patchy.patch(sample, """\
                @@ -2,2 +2,2 @@
                -    return 1
                +    return 2""")
        
            print(sample())  # prints 2
        
        
        ``unpatch(func, patch_text)``
        -----------------------------
        
        Unapply the patch ``patch_text`` from the source of function ``func``. This is
        the reverse of ``patch()``\ing it, and calls ``patch --reverse``.
        
        The same error and formatting rules apply as in ``patch()``.
        
        Example:
        
        .. code-block:: python
        
            import patchy
        
            def sample():
                return 2
        
            patchy.unpatch(sample, """\
                @@ -2,2 +2,2 @@
                -    return 1
                +    return 2""")
        
            print(sample())  # prints 1
        
        
        ``temp_patch(func, patch_text)``
        --------------------------------
        
        Usable as a context manager or function decorator to wrap code with a call to
        ``patch`` before and ``unpatch`` after.
        
        Context manager example:
        
        .. code-block:: python
        
            def sample():
                return 1234
        
            patch_text = """\
                @@ -1,2 +1,2 @@
                 def sample():
                -    return 1234
                +    return 5678
                """
        
            with patchy.temp_patch(sample, patch_text):
                print(sample())  # prints 5678
        
        Decorator example, using the same ``sample`` and ``patch_text``:
        
        .. code-block:: python
        
            @patchy.temp_patch(sample, patch_text)
            def my_func():
                return sample() == 5678
        
            print(my_func())  # prints True
        
        
        How to Create a Patch
        =====================
        
        1. Save the source of the function of interest in a ``.py`` file, e.g.
           ``before.py``. Make sure you dedent it so there is no whitespace before the
           ``def``:
        
           .. code-block:: python
        
               def foo():
                   print("Change me")
        
        2. Copy that ``.py`` file, to e.g. ``after.py``, and make the changes you
           want:
        
           .. code-block:: python
        
               def foo():
                   print("Changed")
        
        3. Run ``diff``, e.g. ``diff before.py after.py``. You will get output like:
        
           .. code-block:: diff
        
              diff --git a/Users/chainz/tmp/before.py b/Users/chainz/tmp/after.py
              index e6b32c6..31fe8d9 100644
              --- a/Users/chainz/tmp/before.py
              +++ b/Users/chainz/tmp/after.py
              @@ -1,2 +1,2 @@
               def foo():
              -    print("Change me")
              +    print("Changed")
        
        4. The filenames are not necessary for ``patchy`` to work. Take only from the
           first ``@@`` line onwards into the multiline string you pass to
           ``patchy.patch()``:
        
           .. code-block:: python
        
              patchy.patch(foo, """\
                  @@ -1,2 +1,2 @@
                   def foo():
                  -    print("Change me")
                  +    print("Changed")
                  """)
        
        
        
        
        History
        -------
        
        1.1.0 (2015-06-16)
        ------------------
        
        * Fixed code compilation to use the ``__future__`` flags from the function that
          is being patched
        * Added ``unpatch`` method
        * Added ``temp_patch`` context manager/decorator
        
        
        1.0.0 (2015-06-09)
        ---------------------
        
        * First release on PyPI, featuring ``patch`` function.
        
Keywords: patchy
Platform: UNKNOWN
Classifier: Development Status :: 5 - Production/Stable
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: BSD License
Classifier: Natural Language :: English
Classifier: Operating System :: OS Independent
Classifier: Programming Language :: Python :: 2
Classifier: Programming Language :: Python :: 2.7
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.4
