Dino Viehland <[email protected]> added the comment:
My actual scenario involves a custom module loader where the modules are
published are completely immutable (it ends up publishing an object which isn't
a subtype of module). It can still have normal Python modules as a child which
aren't immutable, so they could still be patched by Mock (or it could have
immutable sub-packages which Mock wouldn't be able to patch).
So imagine something like this:
immutable_package\__init__.py
__immutable__ = True
x = 2
immutable_package\x.py
y = 2
Doing a "from immutable_package import x" would normally publish "x" as a child
onto the package. But because the package is immutable, this is impossible,
and the assignment is ignored with a warning.
When Mock gets a call to patch on something like "immutable_package.x.y", it's
not going to find x, even though if I were to write "from immutable_package.x
import y" or "from immutable_package import x" it would succeed.
Cases can be contrived without all of this though where the child isn't
published on it's parent, but it requires
x/__init__.py
from x.pkg import child
x/pkg/__init__.py:
x = 1
x/pkg/child.py:
from unittest.mock import patch
y = 42
@patch('x.pkg.child.y', 100)
def f():
print(y)
f()
"python -m x" will fail without the patch but succeed with it.
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Python tracker <[email protected]>
<https://bugs.python.org/issue39551>
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