PyCQA / PyCQA/pyflakes

Pyflakes doesn't properly handle del inside function definition

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Python
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Description

a = 1

def test():
    a = 2
    del a
    print(a)

test()

The code produces UnboundLocalError: local variable 'a' referenced before assignment, but pyflakes shows now errors.

The reason this code raises an exception is that local variables are determined statically at compile time, not at runtime, so the a = 2 line forces a to be function local inside of test. The del a does not make it global again (it is impossible to "make a local variable global again").

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running Pyflakes on the example code in the issue and trace how function-local assignments and del a are handled. Done means Pyflakes reports the invalid later use of a, with a regression test covering this example; no source file or test path is named in the issue.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
tooling
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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