Missing W0612: Unused variable warning if exception name is being reused

[ptagl]

Bug description

Save the following code in a file like pylint_test.py.

"""
Dummy module.
"""

def my_function():
    """
    Dummy function.
    """

    try:
        my_var = 1/0
    except ZeroDivisionError as exception:
        assert exception

    try:
        my_var = 1/0
    except ZeroDivisionError as exception:
        # The following line makes "exception" unused
        #pass
        # For the second run, comment the line above and uncomment the line below
        print(exception)
        # Why "exception" at line 26 is not marked as unused?

    try:
        my_var = 1/0
    except ZeroDivisionError as exception:
        pass

    print(my_var)

my_function()

Configuration

No response

Command used

pylint pytlint_test.py

Pylint output

`pylint_bug.py:17:4: W0612: Unused variable 'exception' (unused-variable)` when line 19 is not commented and line 21 is commented, nothing when line 19 is commented and line 21 is not.

Expected behavior

I would expect to get a "unused variable" warning for line 26 at least when commenting line 19 and uncommenting line 21, like:

pylint_test.py:26:4: W0612: Unused variable 'exception' (unused-variable)

Pylint version

pylint 2.13.2

OS / Environment

Opensuse Tumbleweed

Additional dependencies

No response

[jacobtylerwalls]

Hi @ptagl, thanks for the writeup. The variables checker warns once per variable per scope. For fishy patterns in the same scope (redefining a variable inside an except handler or nested loop) we have redefined-outer-name, but still no further messages for unused-variable.

For instance, just one warning is emitted for:

def a():
    x = 0  # [unused-variable]
    x = 0

If you have thoughts I'd be happy to continue discussing on #4391. Thanks for opening the ticket; it forced me to go back through that discussion again.

[jacobtylerwalls]

Oh, by the way, we also have #5838 open for warning about "dead stores" of reassigning "as e" and doing nothing with it. That's probably the better superseder.

[ptagl]

@jacobtylerwalls thanks a lot for your answers, it's ok for me to close this issue: I'm not a Python expert, so I'm not sure what a linter should or should not report.

By the way, I just wanted to let you know that I've found that both Flake8 and Pyflakes correctly detect the unused variable in my example, not sure if such information is useful or not.

[jacobtylerwalls]

Interesting. I had a look and it turns out that pyflakes is actually unsatisfied with their handling of this, so although your example works, they are issuing false positives, see PyCQA/pyflakes#378.