scoping rule for nested-loop in python

Question

def temp():
    temparray = ['a','b']
    temparray_2 = ['c','d','e']
    for i in temparray:
        print('i:' + str(i))
        for i in temparray_2:
            print('first: ' + str(i))
        print('Second: ' + str(i))

    print('final: ' + str(i))

Why does the above code the following output? The variable i seems to get overwritten by whatever that is last assigned in the inner loop. Does python not obey the scoping rule like Java or C?

i:a
first: c
first: d
first: e
Second: e
i:b
first: c
first: d
first: e
Second: e
final: e

I would avoid using the same variable in nested for statements. If you want one to influence the other, use an assignment. — Ctrl S
– Ctrl S, Commented May 29, 2018 at 18:15
Yes, Python doesn't work like Java/C. You can find a simple explanation of these rules here. The important bit: "Each assignment or import statement occurs within a block defined by a class or function definition or at the module level (the top-level code block)." Note, that only function definitions, class definitions, and the module create a block with their own scope. Nothing else does. Not for-loops, or if-statements etc. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented May 29, 2018 at 18:21

chepner · Accepted Answer · 2018-05-29 17:54:11Z

3

Like any function-local assignment, the loop index is in scope for the entire function the for loop appears in. A for loop itself does not create a new scope.

answered May 29, 2018 at 17:54

chepner

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4 Comments

Mad Physicist Over a year ago

Also, a for statement represents an assignment operation.

chepner Over a year ago

@MadPhysicist That's what I mean to infer, but I don't think I could have been less explicit :)

Mad Physicist Over a year ago

infer->imply? :)

chepner Over a year ago

I'm going to stop typing now.

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