Python built in max() function shadowed by variable of same name appearing later in the program

Asked May 01 '20 at 12:56

Active May 01 '20 at 12:56

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I got a python error that surprised me this morning. Consider this simple example:

def f(mylist):
    m = max(mylist)
    max = m

I expected this function to execute without failing, but it throws:

UnboundLocalError: local variable 'max' referenced before assignment

I assumed that since python was an interpreted language, overwriting the built-in max() function wouldn't cause any trouble as long as I didn't try to invoke it again afterwards.

Why does this behavior occur? Does the python interpreter "look ahead" for variable declarations?

asked May 01 '20 at 12:56

PotatoBoy

Use `max1` instead of `max` as `max1 = m`. – Abhay Salvi May 01 '20 at 13:00
For a more detailed look at Python scoping rules, see [this question](https://stackoverflow.com/questions/291978/short-description-of-the-scoping-rules). – Mihai Chelaru May 01 '20 at 13:04

Python built in max() function shadowed by variable of same name appearing later in the program

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