Use before assignment not detected

[Hibou57]

Steps to reproduce

Check this with Pylint:

def test(a):
    if a == 1:
        b = 2
    return 3 if b else 4

Current behavior

Does not warn b is used without (very probably) being assigned (more below).

Expected behavior

Opinions may vary, still here is mine: I know too many false alerts is at the detriment of alerts in the large. I know there use to be a Borland C++ compiler triggering annoying and noisy warnings when an assignment was conditional, which seems to be a case very close to this one. But there is only one condition, so clearly it can’t cover all cases. The probability b is not assigned, is high.

pylint --version output

pylint 1.7.4,
astroid 1.5.3
Python 3.5.2 (default, Nov 23 2017, 16:37:01)
[GCC 5.4.0 20160609]

Note

I’m not telling about it as a bug, rather a an hint.

[PCManticore]

This makes sense, but we could only detect it in a sane manner once we land control flow support in pylint.

[Hibou57]

@PCManticore , don’t worry too much, PyLint is already very clever even without it.

[jacobtylerwalls]

Duplicate of #1727 and #267.

[Pierre-Sassoulas]

Closing as a duplicate of #1727, it's old but the discussion happened elsewhere. (Thank you @jacobtylerwalls for helping us cleanup)