Mock library for Python, return value only once in mocked function?

Question

Mocking a method with mock is simple enough, for instance, like this:

o.get_idlist = mock.Mock(return_value=[1])

However, that will make get_idlist() return [1] every time. Is there a way to make it return [1] only once, and subsequent calls return [] (for instance) without using side_effect=somefun?  I guess what I want is a kind of side effect, but there you go.

(I just think it's so clumsy to create a big honking named function just for that... or is there a way to use a lambda here?)

F. Pareto · Answer

Assuming you don't have anything against side_effect itself but just don't want to create a whole function, you could roughly do something like the following

>>> from unittest.mock import Mock
>>> m = Mock()
>>> m.side_effect = [1] + [[]]*100
>>> m() 
1
>>> m()
[] 
>>> m()
[]
>>> m()
[]
>>> m()
[]

I admit it's a bit dirty but if you just want to make a quick test it should be sufficient. Of course you could replace [] with [0] or whatever you like.

jvallver · Answer

I think the only way to do what you want with python-mock library is using a side_effect.
I can give you an alternative:
Take a look to mockito library.
With it is easy to make what you want:
from mockito import when

when(o).get_idlist().thenReturn([1]).thenReturn([])

Mock library for Python, return value only once in mocked function?

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