Allow Redefinitions of For Loop Iteration Variables

[rameshvarun]

Bug Report

MyPy has a flag --allow-redefinition to enable variable redefinition in limited circumstances. This doesn't seem to work with variables bound in a for loop iteration.

To Reproduce

https://mypy-play.net/?mypy=1.5.1&python=3.11&flags=allow-redefinition&gist=005972804edd5316ace18ea835fb9f52

for i in range(3):
    i: str = str(i)
    reveal_type(i)
    
def test(i: int):
    i: str = str(i)
    reveal_type(i)

Expected Behavior

Both cases are allowed.

Actual Behavior

MyPy throws an error only for line 2.

main.py:2: error: Name "i" already defined on line 1  [no-redef]
main.py:3: note: Revealed type is "builtins.int"
main.py:7: note: Revealed type is "builtins.str"
Found 1 error in 1 file (checked 1 source file)

Your Environment

MyPy Version v1.5.1

[rameshvarun]

This snippet poses problems - at the end, the type of i is still <class 'int'>.

try:
    for i in range(3):
        function_that_throws()
        i: str = str(i)
except:
    pass
    
print(type(i))

So i can only be considered a string within the remaining statements of the for loop body. Not sure if MyPy has the features to make this possible?

[Avasam]

Here's another real world example: https://github.com/pypa/distutils/pull/343/files#r2440199822
Permalink: https://github.com/Avasam/distutils/blob/5033f535389617000c6a43d93b33a4f534fa2e73/distutils/fancy_getopt.py#L251-L278