bpo-44730: Add handling of generator functions

[gmjw]

Previously generator functions were changed by patches applied as decorators, ending up as non-generator functions (co_flags changed from 99 to 31). Patches were not applied properly in these generator functions.

This PR addresses this by adding a simple switch in mock.py to handle generator functions cleanly.

https://bugs.python.org/issue44730

[the-knights-who-say-ni]

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[gmjw]

I would be happy to flesh these changes out with a test or two, of course - there is an example associated with the bug report which could easily be made into a simple unit test.

I've never contributed to the repo before so I'll await some general feedback before proceeding with anything.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[isidentical]

This doesn't preserve the original characteristics. For example on the following function

def gen_1():
    yield 1
    return 2

this will simply raise StopIteration(None) instead of StopIteration(2) at the end. You should return the result of the generator (see PEP 380)

[gmjw]

You're absolutely right. Thanks, I forgot that generator functions could also return values.

[MaxwellDupre]

I can't get this to run correctly:

./python -m unittest Lib/unittest/test/testmock/testpatch.py
Traceback (most recent call last):
File "/home/me/Documents/cpython/Lib/importlib/init.py", line 16, in
import _frozen_importlib as _bootstrap
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ModuleNotFoundError: import of _frozen_importlib halted; None in sys.modules

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "", line 198, in _run_module_as_main
File "", line 88, in _run_code
File "/home/me/Documents/cpython/Lib/unittest/main.py", line 18, in
main(module=None)
^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/unittest/main.py", line 100, in init
self.parseArgs(argv)
^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/unittest/main.py", line 147, in parseArgs
self.createTests()
^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/unittest/main.py", line 158, in createTests
self.test = self.testLoader.loadTestsFromNames(self.testNames,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/unittest/loader.py", line 198, in loadTestsFromNames
suites = [self.loadTestsFromName(name, module) for name in names]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/unittest/loader.py", line 198, in
suites = [self.loadTestsFromName(name, module) for name in names]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/unittest/loader.py", line 132, in loadTestsFromName
module = import(module_name)
^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/unittest/test/testmock/testpatch.py", line 13, in
from test.test_importlib.util import uncache
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/test/test_importlib/util.py", line 96, in
source_importlib = import_importlib('importlib')['Source']
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/test/test_importlib/util.py", line 52, in import_importlib
source = import_helper.import_fresh_module(module_name, fresh=fresh,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/contextlib.py", line 153, in exit
self.gen.throw(typ, value, traceback)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/test/support/import_helper.py", line 26, in _ignore_deprecated_imports
yield
^^^^^
File "/home/me/Documents/cpython/Lib/contextlib.py", line 153, in exit
self.gen.throw(typ, value, traceback)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/test/support/import_helper.py", line 102, in frozen_modules
yield
^^^^^
File "/home/me/Documents/cpython/Lib/test/support/import_helper.py", line 159, in import_fresh_module
return importlib.import_module(name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/importlib/init.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/importlib/init.py", line 19, in
_bootstrap._setup(sys, _imp)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/importlib/_bootstrap.py", line 1247, in _setup
loader._setup_module(module)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/me/Documents/cpython/Lib/importlib/_bootstrap.py", line 829, in _setup_module
assert not hasattr(module, 'file'), module.file
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: /home/me/Documents/cpython/Lib/zipimport.py

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How to you test testpatch?