The line where the original attributes are backed up needs to be a deep copy (otherwise the updates will affect the backed up dictionary):

self.orig = self.obj.__dict__

Should be more like:

self.orig = self.obj.__dict__.copy()

Agreed. I did the following:

    def __enter__(self):
        self.original = dict(self.obj.__dict__)
        self.obj.__dict__.update(self.mocks)
        return self

    def __exit__(self, typ, val, traceback):
        self.obj.__dict__ = self.original

This doesn't perform a deep copy, but prevents modifications on self.obj.__dict__ from modifying self.original also.

   self.mocks = dict(zip(args[::2], args[1::2]))

Makes for a very unpythonic feeling API. I’d be interested to hear why the author settled on this design, and see example uses that he likes the look of. Are there any other libraries which use this pattern?

You can either use mock(obj, {'x': 1, 'y': 2}) or mock(obj, 'x', 1, 'y', 2). I thought it'll be nice to provide both options, but you might be right and using just a dict of mocks is more Pythonic.

At risk of bikeshedding, I think the "most pythonic" approach would be mock(obj, x=1, y=2)

Seriously though, cool lib, thanks for it =)

Yes, the most pythonic is:

  mock(obj, x=1, y=2)

Which you get by:

  def __init__(self, obj, **mocks):
      self.obj = obj
      self.mocks = mocks

This can then also be called (using the built-in double-star-unpacking feature) as:

  mock(obj, **{'x': 1, 'y': 2})

or even

  mock(obj, **dict([('x', 1), ('y', 2)]))

Then there’s no explicit need to support multiple alternative function signatures, and in particular you don’t get people using the (quite atypical and therefore semantically ambiguous):

  mock(obj, 'x', 1, 'y', 2).

Thanks, updated the code to use keyword arguments only.

For another clever take on mocking in Python, check out Ian Bicking's minimock: http://blog.ianbicking.org/minimock.html

I'm getting more intimate with Python and also made a small mocking library, I'm looking for constructive feedback: https://github.com/paolovictor/mockaccino