Steven D'Aprano <steve+pyt...@pearwood.info> added the comment:
Here's an example that shows what is going on:
def demo():
a = 1
class B:
x = a
print(B.x) # Okay.
class C:
x = a # Fails.
if False:
a = None
print(C.x)
If you run that, B.x is printed (1) but assigning to C.x fails:
>>> demo()
1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 7, in demo
File "<stdin>", line 8, in C
NameError: name 'a' is not defined
The reason is that inside a function, assignment to a name makes it a local.
This interacts oddly with class scope.
By the way, I get the same results with this all the way back to Python 2.4. (I
don't have older versions to test.) So this has existed for a very long time.
----------
nosy: +steven.daprano
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<https://bugs.python.org/issue43380>
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