Patching out modules in Python

gistfile1.py

import contextlib
import collections
import mock
import sys

def fake_module(**args):
    return (collections.namedtuple('module', args.keys())(**args))

def get_patch_dict(dotted_module_path, module):
    patch_dict = {}
    module_splits = dotted_module_path.split('.')

    # Add our module to the patch dict
    patch_dict[dotted_module_path] = module

    # We add the rest of the fake modules in backwards
    while len(module_splits) > 1:
        # This adds the next level up into the patch dict which is a fake
        # module that points at the next level down
        patch_dict['.'.join(module_splits[:-1])] = fake_module(
            **{module_splits[-1]: patch_dict['.'.join(module_splits)]}
        )
        module_splits = module_splits[:-1]

    return patch_dict

with mock.patch.dict(
    sys.modules,
    get_patch_dict('herp.derp', fake_module(foo='bar'))
):
    import herp.derp
    # prints bar
    print herp.derp.foo