[issue40805] Can no longer patch flask.g

[Rob Taft]

Rob Taft  added the comment:

https://github.com/pallets/flask/issues/3637

I've worked around the issue and accept that this will not work in the future.

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[issue40805] Can no longer patch flask.g

[Rob Taft]

Rob Taft  added the comment:

I updated the test with 2 cases and the traceback is different for each when I 
expected them to be the same if this was purely a mock issue, the line throwing 
the error is the same.  I can post this over with flask and see what they think.

from unittest.mock import patch

import flask

def some_function():
flask.g.somevariable = True
return flask.g.somevariable

@patch('flask.g')
def test_patch(mock_flask_global):
assert some_function()

def test_no_patch():
assert some_function()


$ pytest -vv temp_test.py 

 test session starts 
=
platform linux -- Python 3.8.3, pytest-5.4.3, py-1.8.1, pluggy-0.13.1 -- 
collected 2 items   

 

temp_test.py::test_patch FAILED 

   [ 50%]
temp_test.py::test_no_patch FAILED  

   [100%]

==
 FAILURES 
==
_
 test_patch 
_

args = (), keywargs = {}

@wraps(func)
def patched(*args, **keywargs):
>   with self.decoration_helper(patched,
args,
keywargs) as (newargs, newkeywargs):

../../../.pyenv/versions/3.8.3/lib/python3.8/unittest/mock.py:1322: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../../.pyenv/versions/3.8.3/lib/python3.8/contextlib.py:113: in __enter__
return next(self.gen)
../../../.pyenv/versions/3.8.3/lib/python3.8/unittest/mock.py:1304: in 
decoration_helper
arg = exit_stack.enter_context(patching)
../../../.pyenv/versions/3.8.3/lib/python3.8/contextlib.py:425: in enter_context
result = _cm_type.__enter__(cm)
../../../.pyenv/versions/3.8.3/lib/python3.8/unittest/mock.py:1416: in __enter__
if spec is None and _is_async_obj(original):
../../../.pyenv/versions/3.8.3/lib/python3.8/unittest/mock.py:51: in 
_is_async_obj
if hasattr(obj, '__func__'):
pyvenv/lib/python3.8/site-packages/werkzeug/local.py:347: in __getattr__
return getattr(self._get_current_object(), name)
pyvenv/lib/python3.8/site-packages/werkzeug/local.py:306: in _get_current_object
return self.__local()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

name = 'g'

def _lookup_app_object(name):
top = _app_ctx_stack.top
if top is None:
>   raise RuntimeError(_app_ctx_err_msg)
E   RuntimeError: Working outside of application context.
E   
E   This typically means that you attempted to use functionality that 
needed
E   to interface with the current application object in some way. To 
solve
E   this, set up an application context with app.app_context().  See the
E   documentation for more information.

pyvenv/lib/python3.8/site-packages/flask/globals.py:45: RuntimeError
___
 test_no_patch 


def test_no_patch():
>   assert some_function()

temp_test.py:14: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
temp_test.py:6: in some_function
flask.g.somevariable = True
pyvenv/lib/python3.8/site-packages/werkzeug/local.py:364: in 
 

[issue40805] Can no longer patch flask.g

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Chris, I see no evidence in the *incomplete* traceback not posted here that 
there is a bug in mock.  Mock calls "hasattr(obj, '__func__') and apparently 
flask, called via werkzeug, answers 'RuntimeError'.  The overt bug is that 
calling werkzeug.local.(type(obj)?).__getattr__ fails by doing something other 
than "return the (computed) attribute value or raise an AttributeError 
exception".
https://docs.python.org/3/reference/datamodel.html#object.__getattr__

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[issue40805] Can no longer patch flask.g

[Rob Taft]

Change by Rob Taft :


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versions: +Python 3.9 -Python 3.6

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[issue40805] Can no longer patch flask.g

[Rob Taft]

Rob Taft  added the comment:

I have confirmed that using unittest.mock instead of the 3rd party mock library 
in python 3.8.3 and 3.9-dev fails to patch flask.g.  3.7.7 works correctly.

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[issue40805] Can no longer patch flask.g

[Chris Withers]

Chris Withers  added the comment:

Rob, you're welcome to dump `mock` and use `unittest.mock`, and that might be 
best for now, but this will then likely come back to bite you when you end up 
on the version of Python, probably 3.9, where it is present ;-)

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[issue40805] Can no longer patch flask.g

[Chris Withers]

Change by Chris Withers :


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[issue40805] Can no longer patch flask.g

[Chris Withers]

Chris Withers  added the comment:

Terry, mock is now a rolling backport of unittest.mock with all development 
taking place in cpython's repo. If issues are reported there, they need to be 
triaged here first, as it's most likely a bug in unittest.mock that needs 
fixing here.

Rob, please can you see if this is reproducible on Python 3.8 or 3.9, replacing 
`from mock import` with `from unittest.mock` import?

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nosy: +cjw296

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[issue40805] Can no longer patch flask.g

[Rob Taft]

Rob Taft  added the comment:

The test was supposed to patch the flask component during the unit test,
the error indicates the patch did not work.  The actual error message is
not relevant to the actual issue. I don't know why I was directed to here.
When I replace it with unittest.mock, it appears to work fine, so my
solution might end up being to dump the 3rd party mock library.

On Fri, May 29, 2020 at 11:02 PM Terry J. Reedy 
wrote:

>
> Terry J. Reedy  added the comment:
>
> Sorry, but I believe you were misdirected*.  mock, as opposed to
> unittest.mock, pytest, flask, and werkzeug  are 3rd party modules.  The
> error report seems to be missing part of the stacktrace at both ends.  What
> line is your file resulted in the error?  (This time we can guess ==
> @patch. @What called _lookup_app_object in flask?  (I have no idea.)
>
> However, once contextlib._GeneratorContextManager calls next(self.gen),
> the rest of the trace is outside the stdlib.  At the end, the RuntimeError
> is raised by flask, not by python, because the flask _app_ctx_stack.top
> does not exist.  If you do not understand their error message, ask flask
> people.
>
> * I assume that cjw296 *glanced* at your report, saw 'RuntimeError', and
> too quickly assumed 'cpython error'.  flask could have defined, for
> instance, FlaskRuntimeError for its error reporting.
>
> --
> nosy: +terry.reedy
> resolution:  -> third party
> stage:  -> resolved
> status: open -> closed
>
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[issue40805] Can no longer patch flask.g

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Sorry, but I believe you were misdirected*.  mock, as opposed to unittest.mock, 
pytest, flask, and werkzeug  are 3rd party modules.  The error report seems to 
be missing part of the stacktrace at both ends.  What line is your file 
resulted in the error?  (This time we can guess == @patch. @What called 
_lookup_app_object in flask?  (I have no idea.)

However, once contextlib._GeneratorContextManager calls next(self.gen), the 
rest of the trace is outside the stdlib.  At the end, the RuntimeError is 
raised by flask, not by python, because the flask _app_ctx_stack.top does not 
exist.  If you do not understand their error message, ask flask people.

* I assume that cjw296 *glanced* at your report, saw 'RuntimeError', and too 
quickly assumed 'cpython error'.  flask could have defined, for instance, 
FlaskRuntimeError for its error reporting.

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nosy: +terry.reedy
resolution:  -> third party
stage:  -> resolved
status: open -> closed

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[issue40805] Can no longer patch flask.g

[Ruairidh MacLeod]

Change by Ruairidh MacLeod :


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[issue40805] Can no longer patch flask.g

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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nosy: +xtreak

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[issue40805] Can no longer patch flask.g

[Rob Taft]

New submission from Rob Taft :

Whenever I try to patch flask.g, it appears to do nothing.  This happened when 
I upgraded mock from 3.x to 4.x.  I reported it on the mock github page 
https://github.com/testing-cabal/mock/issues/490 and was asked to report it 
here.  The folllowing code run with pytest works fine in mock 3.0.5, but fails 
to patch in 4.0.0 and up.

from mock import patch

import flask


def some_function():
flask.g.somevariable = True
return flask.g.somevariable


@patch('flask.g')
def test_some_function(mock_flask_global):
assert some_function()

--
components: Tests
messages: 370197
nosy: Rob Taft
priority: normal
severity: normal
status: open
title: Can no longer patch flask.g
type: behavior
versions: Python 3.6, Python 3.8

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