Why does Python for-loop shadowing break outer function? [duplicate]

Code

Initially, I have some instances of classes stored in a dictionary, each with some initialized attribute.

class A:
    def __init__(self):
        self.foo = 'bar'

my_dict = {}

for i in range(3):
    my_dict[i] = A()

Now, I call a function on a dictionary value, my_dict[1], say, wanting to change the .foo attributes of all values in the dictionary, except that of my_dict[1], which I would like to change differently.

def outer(v):
    for k,v in my_dict.items():
        my_dict[k].foo = 'nada'
    v.foo = 'sand'

my_entry = my_dict[1]

outer(my_entry)

print(list((k,v.foo) for (k,v) in my_dict.items()))

However, the third line under outer(v) ends up changing my_dict[2].foo instead.

Problem

Consider the three lines in the function outer(v), and the output from the print(...).

• Without first two lines, gives [(0, 'bar'), (1, 'sand'), (2, 'bar')] as expected.
• Without third line, gives [(0, 'nada'), (1, 'nada'), (2, 'nada')] as expected.
• However, with all three lines, gives [(0, 'nada'), (1, 'nada'), (2, 'sand')].

This suggests the variable v has been 'stuck' at index 2, following exit from for-loop. Why does Python do this?

Background

This problem caused a huge hold-up in a larger program I was making. This is my first attempt at asking a question on Stack Overflow by making a minimal, reproducible example. Any advice on how to make the question clearer or better is very much appreciated. Thank you.