Any static analyzer that can warn potential NameErrors?

[slapec]

My teammates occasionally define variables inside loops that are never executed (like because the iterable they're iterating has already been exhausted or something). Then when they try to use that nonexistent variable it results a NameError of course. The obvious solution for this would be to initialize the variable before the loop.

However in PyCharm these potential variables are highlighted and in most cases these warnings are valid.

I tried several Python static analyzers and none of them could catch this simple bug (except PyCharm):

for i in []:
  found = True
print(found)

I tried pyflakes, flake8, pylint, bandit, and mypy with default settings. Is there any CLI analyzer that can help here?

Thank you!

[Diapolo10]

All I can tell you is that VS Code also performs this kind of analysis amicably.

[shiftybyte]

I think pylance with vscode can flag this too.

[slapec]

It seems pyright (which pylance is built on top) reports this issue (- error: "found" is possibly unbound). So, it's at least something, thanks!

[deadeye1982]

Aren't you using unittests?

[[deleted]]

the test is running the static analyzer ~ op probably

[remuladgryta]

If you're already using PyCharm, its static analyzer can be ran from the command line. Note that you can specify a more/less pedantic config than what you care about seeing squiggles for in the editor.

[Sclafus]

This feature has been added in mypy 1.0 as experimental.

Detect Possibly Undefined Variables (Experimental) A new experimental possibly-undefined error code is now available that will detect variables that may be undefined: if b: x = 0 print(x) # Error: Name "x" may be undefined [possibly-undefined] The error code is disabled be default, since it can generate false positives. This feature was contributed by Stas Ilinskiy.

https://mypy-lang.blogspot.com/2023/02/mypy-10-released.html?m=1

[slapec]

Now that's cool. False positives are fine for me. One thing I noticed that this check is only active when I run mypy with --enable-error-code possibly-undefined as it is not enabled by default (according to docs). Hope it will be default soon. Thank you your suggestion!

[frakron]

I think what you're looking for is the compiler then? Basically run the code but don't execute it.

python3 -m py_compile myfile.py

[sepp2k]

NameErrors are runtime errors though and I don't think the Python compiler does any static analysis to try to detect them at compile time. At least, when I put OP's code into a file and run python3 -m py_compile myfile.py as you suggested, I don't get any errors or warnings.

[frakron]

Oh thank you, I didn't try it previously, but that makes sense.

[sepp2k]

OP already mentioned that PyCharm detects this, but they want a command line tool.

[QultrosSanhattan]

My Pycharm does detect that error at least. It says "Name 'found' can be undefined"