Can a mock side_effect iterator be reset after it has been exhausted?

Question

mock.reset_mock() will not reset a side effect iterator. Is there a way to do this without creating the mock again?

>>> from mock import MagicMock
>>> mock = MagicMock(side_effect = [1,2])
>>> mock(), mock()
(1, 2)
>>> mock()

Traceback (most recent call last):
  File "<pyshell#114>", line 1, in <module>
    mock()
  File "C:\Python27\Lib\site-packages\mock.py", line 955, in __call__
    return _mock_self._mock_call(*args, **kwargs)
  File "C:\Python27\Lib\site-packages\mock.py", line 1013, in _mock_call
    result = next(effect)
StopIteration
>>> mock.reset_mock()
>>> mock()

Traceback (most recent call last):
  ...
StopIteration
>>> mock = MagicMock(side_effect = [1,2])
>>> mock(), mock()
(1, 2)
>>> 

The intent is to re-use the mock in subsequent tests but I suspect that, like a generator, it cannot be restarted.

So (better late than never) after being pointed in the right direction I looked in mock.py and found that side_effect is an iterator object (which cannot be reset once exhausted):

def __set_side_effect(self, value):
    value = _try_iter(value)
    ...

def _try_iter(obj):
    ...
    try:
        return iter(obj)
    except TypeError:
        # XXXX backwards compatibility
        # but this will blow up on first call - so maybe we should fail early?
        return obj

and def reset_mock() does not address the side efect.

Answer 1

Note that since Python 3.6, you can reset the mock side_effect and return_value with:

mock.reset_mock(return_value=True, side_effect=True)

From the docs:

In case you want to reset return_value or side_effect, then pass the corresponding parameter as True. Child mocks and the return value mock (if any) are reset as well.

Answer 2

As user2357112 commented, reassigning side_effect will solve you problem.

>>> from mock import MagicMock
>>>
>>> lst = [1, 2]
>>> mock = MagicMock(side_effect=lst)
>>> mock(), mock()
(1, 2)
>>> mock.side_effect = lst  # <-------
>>> mock(), mock()
(1, 2)