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Title: side_effect mocked method lose reference to instance
Type: enhancement Stage: resolved
Components: Library (Lib) Versions: Python 3.8, Python 3.7
Status: closed Resolution: not a bug
Dependencies: Superseder:
Assigned To: Nosy List: Adnan Umer, cjw296, mariocj89, remi.lapeyre, xtreak
Priority: normal Keywords:

Created on 2018-12-24 15:19 by Adnan Umer, last changed 2022-04-11 14:59 by admin. This issue is now closed.

Messages (3)
msg332463 - (view) Author: Adnan Umer (Adnan Umer) Date: 2018-12-24 15:19
When a method/bounded function is mocked and side_effect is supplied to it, the side_effect function doesn't get the reference to the instance.

Suppose we have something like this

class SomeClass:
    def do_something(self, x):

def some_function(x):
    cls = SomeClass()
    y = class.do_something(x)
    return y

And the test for some_function will be 

def do_something_side_effect(x):
    retrun x

def test_some_function():
    with mock.path("SomeCass.do_something") as do_something_mock:
        do_something_mock.side_effect = do_something_side_effect
        assert some_function(1)

Here do_something_side_effect mock will not have access to SomeClass instance.
msg332848 - (view) Author: Rémi Lapeyre (remi.lapeyre) * Date: 2019-01-02 00:41
Is there a problem with:

from unittest import mock

class SomeClass:
    def do_something(self, x):

def some_function(x):
    obj = SomeClass()
    y = obj.do_something(x)
    return y

def do_something_side_effect(self, x):
    return x

def test_some_function():
    with mock.patch.object(SomeClass, "do_something", do_something_side_effect):
        assert some_function(1)

msg335548 - (view) Author: Karthikeyan Singaravelan (xtreak) * (Python committer) Date: 2019-02-14 18:04
Thanks for the report. I think this is design by choice that self is not passed to the side_effect directly set on the mock [0]. Changing this would break existing tests like [1] . You can use the approach by @remi.lapeyre which directly replaces the function on the target inside the context manager at [2] passing self to the side_effect callable.

Date User Action Args
2022-04-11 14:59:09adminsetgithub: 79758
2022-03-19 19:47:30iritkatrielsetstatus: open -> closed
resolution: not a bug
stage: resolved
2019-02-14 18:04:09xtreaksetnosy: + cjw296, xtreak, mariocj89

messages: + msg335548
versions: - Python 2.7, Python 3.4, Python 3.5, Python 3.6
2019-01-02 00:41:13remi.lapeyresetnosy: + remi.lapeyre
messages: + msg332848
2018-12-24 15:19:00Adnan Umercreate