Example where pylint does not detect uninitialized variable

[socketpair]

def test():
    try:
        with open('xxxxx', 'rt') as config_file:
            old_settings: str = config_file.read()
    except FileNotFoundError:
        print(old_settings)

Pylint should report that old_settings might not be initialized. Since initialization is the last operation in try...except block, any exception prevents initialization.

[hippo91]

@socketpair thanks for the report. It makes sense.

[jacobtylerwalls]

On main, this is only reproducible because of the context manager, which fails the following check (the context manager gets between the assignment and the TryExcept, so the TryExcept is actually two parents up):

https://github.com/PyCQA/pylint/blob/52576b7552b68593a3ea28e20cd3751ccdc106d7/pylint/checkers/variables.py#L686

[DanielNoord]

Might be fixable with checkers.utils.get_node_first_ancestor_of_type?

[jacobtylerwalls]

You can assign this to me, I'll give it a spin and report back.

[markmark206]

And what about this case (should I open a separate issue?):

$ cat use_before_assignment.py
def compute() -> int:
    raise ValueError("bad chickens")

def count_chickens():
    try:
        chicken_count = compute()
    except ValueError:
        print(chicken_count)

count_chickens()

$ pylint -d missing-module-docstring,missing-function-docstring use_before_assignment.py

--------------------------------------------------------------------
Your code has been rated at 10.00/10 (previous run: 10.00/10, +0.00)

$ pylint --version
pylint 2.12.2
astroid 2.9.3
Python 3.9.9 (v3.9.9:ccb0e6a345, Nov 15 2021, 13:06:05)
[Clang 13.0.0 (clang-1300.0.29.3)]

$ python use_before_assignment.py
Traceback (most recent call last):
  File "/Users/markgenba/src/genba/use_before_assignment.py", line 6, in count_chickens
    chicken_count = compute()
  File "/Users/markgenba/src/genba/use_before_assignment.py", line 2, in compute
    raise ValueError("bad chickens")
ValueError: bad chickens

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/markgenba/src/genba/use_before_assignment.py", line 10, in <module>
    count_chickens()
  File "/Users/markgenba/src/genba/use_before_assignment.py", line 8, in count_chickens
    print(chicken_count)
UnboundLocalError: local variable 'chicken_count' referenced before assignment

[DanielNoord]

@markmark206 This actually does emit a warning on the to-be-released 2.13 version thanks to the work of @jacobtylerwalls and others!

[markmark206]

@DanielNoord this is very exciting, thank you!!

I opened a separate issue before i saw this, I will go ahead and close (unless you get there before me).

Thank you again!!