========
backcall
========

.. image:: https://travis-ci.org/takluyver/backcall.png?branch=master
        :target: https://travis-ci.org/takluyver/backcall

Specifications for callback functions passed in to an API

If your code lets other people supply callback functions, it's important to
specify the function signature you expect, and check that functions support that.
Adding extra parameters later would break other peoples code unless you're careful.

backcall provides a way of specifying the callback signature using a prototype
function::

    from backcall import callback_prototype
    
    @callback_prototype
    def handle_ping(sender, delay=None):
        # Specify positional parameters without a default, and keyword
        # parameters with a default.
        pass
    
    def register_ping_handler(callback):
        # This checks and adapts the function passed in:
        callback = handle_ping.adapt(callback)
        ping_callbacks.append(callback)

If the callback takes fewer parameters than your prototype, *backcall* will wrap
it in a function that discards the extra arguments. If the callback expects
more arguments, a TypeError is thrown when it is registered.

For more details, see the `docs <http://backcall.readthedocs.org/en/latest/>`_ or
the `Demo notebook <http://nbviewer.ipython.org/github/takluyver/backcall/blob/master/Demo.ipynb>`_.

The tests are run with `pytest <http://pytest.org/latest/>`_. In the root directory,
execute::

    py.test