[issue44922] isinstance breaks on imported dataclasses
Eric V. Smith added the comment:
You're importing main.py twice. The first is when you run "python main.py",
where it has the module name '__main__'. The second time is in codegen.py,
where it has the name 'main'. You create the AtomX instance as __main__.AtomX,
but the isinstance check is against main.AtomX. Because the objects have
different modules, they're not equal.
You can see this if you change the isinstance check to:
=
from main import AtomX
import sys
def inheritance_map(candidate):
assert isinstance(candidate, sys.modules['__main__'].AtomX)
==
Another way to see this if you add a print statement to the original codegen.py:
==
from main import AtomX
def inheritance_map(candidate):
print(f'{candidate=} {type(candidate)=} {AtomX=}')
assert isinstance(candidate, AtomX)
==
Which will print:
candidate=AtomX(my_symbol='qwerty', quantity='') type(candidate)= AtomX=
Notice the types refer to different modules, so they are distinct and unequal.
The easiest way around this is to not do any work in main.py, but instead
create another module, import it from main.py, and do the work there.
--
resolution: -> not a bug
stage: -> resolved
status: open -> closed
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[issue44922] isinstance breaks on imported dataclasses
Oleg Baskakov added the comment:
Sorry, I forgot to add if __name__ line:
```
import codegen
from dataclasses import dataclass
@dataclass
class AtomX:
my_symbol: str
quantity: str = ""
if __name__ == "__main__":
codegen.inheritance_map(AtomX("qwerty"))
```
So the output:
```
Traceback (most recent call last):
File "/Users/baskakov/PycharmProjects/main.py", line 11, in
codegen.inheritance_map(AtomX("qwerty"))
File "/Users/baskakov/PycharmProjects/codegen.py", line 5, in inheritance_map
assert isinstance(candidate, AtomX)
AssertionError
```
--
Added file: https://bugs.python.org/file50221/main.py
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[issue44922] isinstance breaks on imported dataclasses
Eric V. Smith added the comment:
I get a circular import error:
Traceback (most recent call last):
File "main.py", line 1, in
import codegen
File "/cygdrive/c/home/eric/codegen.py", line 1, in
from main import AtomX
File "/cygdrive/c/home/eric/main.py", line 9, in
codegen.inheritance_map(AtomX("qwerty"))
AttributeError: partially initialized module 'codegen' has no attribute
'inheritance_map' (most likely due to a circular import)
So I can't reproduce this problem.
--
nosy: +eric.smith
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[issue44922] isinstance breaks on imported dataclasses
New submission from Oleg Baskakov :
Hey I was trying to import dataclasses from another file and somehow isinstance
doesn't work anymore:
main.py:
```
import codegen
from dataclasses import dataclass
@dataclass
class AtomX:
my_symbol: str
quantity: str = ""
codegen.inheritance_map(AtomX("qwerty"))
```
codegen.py:
```
from main import AtomX
def inheritance_map(candidate):
assert isinstance(candidate, AtomX)
```
PS the same code with `assert candidate.__class__.__name__ == "AtomX"` works
fine
Python 3.9.6 (v3.9.6:db3ff76da1, Jun 28 2021, 11:49:53)
[Clang 6.0 (clang-600.0.57)] on darwin
I'm running inside of PyCharm
--
messages: 399628
nosy: baskakov
priority: normal
severity: normal
status: open
title: isinstance breaks on imported dataclasses
type: behavior
versions: Python 3.9
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