[issue28733] Show how to use mock_open in modules other that __main__

[Michał Bultrowicz]

Michał Bultrowicz added the comment:

One more update - I had the problem, because I was using monkeypatch.setattr() 
from Pytest, and assumed that it will work the same as patch(). This assumption 
turned out to be wrong.

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[issue28733] Show how to use mock_open in modules other that __main__

[Michał Bultrowicz]

Changes by Michał Bultrowicz :


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status: open -> closed

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[issue28733] Show how to use mock_open in modules other that __main__

[Michał Bultrowicz]

Michał Bultrowicz added the comment:

Ok, I've checked again and now patching "file_writer.open" works. I have no 
idea what I was doing wrong the last time I checked... So I guess I'll close 
the issue.

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[issue28733] Show how to use mock_open in modules other that __main__

[Michał Bultrowicz]

Michał Bultrowicz added the comment:

Then where it should be patched in? Can you give an example? From what I've 
checked patching only works in __main__ and builtins.

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[issue28733] Show how to use mock_open in modules other that __main__

[Michael Foord]

Michael Foord added the comment:

open shouldn't always be patched in builtins, it's much better to patch it in 
the specific namespace it's being called from. So the doc patch here shouldn't 
be applied as is.

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[issue28733] Show how to use mock_open in modules other that __main__

[Berker Peksag]

Berker Peksag added the comment:

Thanks for the report and for the patch. I think expanding the "Where to patch" 
[1] section would be better. We can then refer to it from the mock_open() 
documentation.


[1] https://docs.python.org/3.6/library/unittest.mock.html#where-to-patch

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nosy: +berker.peksag, michael.foord
stage:  -> patch review
versions:  -Python 3.3, Python 3.4

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[issue28733] Show how to use mock_open in modules other that __main__

[Michał Bultrowicz]

New submission from Michał Bultrowicz:

Documentation of mock_open doesn't say how to use it in real-life test 
situations (when you're probably not mocking in __main__). I've spent some time 
scratching my head and googling for the way to mock-out the "open" function, 
want to spare other people the hassle.

The thing is that "open" needs to be mocked out from the magical "builtins" 
module, and not from the place of usage (like when mocking everything that's 
not built-in). So it's not obvious how to do that, especially that the example 
with __main__ makes it look like the normal mocking approach should work.

I still don't fully understand why mocking "__main__.open" can work from 
interpreter, but that's a different thing...

--
assignee: docs@python
components: Documentation
files: mock_open_doc.patch
keywords: patch
messages: 281114
nosy: butla, docs@python
priority: normal
severity: normal
status: open
title: Show how to use mock_open in modules other that __main__
type: enhancement
versions: Python 3.3, Python 3.4, Python 3.5, Python 3.6, Python 3.7
Added file: http://bugs.python.org/file45533/mock_open_doc.patch

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