CODEWITHSUNDEEP
pythonfunctionexceptionscopepycharm
noob overflow
noob overflow

Reputation: 955

Local variable 'result' might be referenced before assignment

With a flow like this:

def func():
    try:
        result = calculate()
    finally:
        try:
            cleanup()
        except Exception:
            pass
    return result

There is a warning about Local variable 'result' might be referenced before assignment:

wat

But I can't really see how that's possible. One of these must be true:

How would you ever get result referenced before assignment? Is there an implementation of calculate and cleanup which could demonstrate that happening?

Upvotes: 4

Views: 2274

Answers (1)

LITzman
LITzman

Reputation: 740

This is a false positive of PyCharms warning heuristics. As per the Python specification, the code behaves as you describe and result can only be reached when set.

According to 8.4 in the Python documentation:

If the finally clause executes a return, break or continue statement, the saved exception is discarded:


>>> def f():
...     try:
...         1/0
...     finally:
...         return 42
...
>>> f()
42

The Python interpreter will ignore the exception that was caused by calculate() if the finally block contains a return, break, or continue statement.

This means that with the implementation you provided, where the finally block has neither of the words specified above, the exception caused by calculate won't be discarded, so the result variable won't be referenced, meaning that this warning is useless.

Upvotes: 3

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