I am trying to use a global variable in a program but getting unexpected results. Example code is shown below. I tried to reduce the problem to its simplest components.

File a.py:

class Foo:
    def __init__(self, s1: str, s2: str):
        self.s1 = s1
        self.s2 = s2

    def __str__(self):
        return f'Foo(s1="{self.s1}", s2="{self.s2}")'

foo = Foo('first', 'second')

def set_foo(new_foo: Foo):
    global foo
    foo = new_foo
    print('Setting foo', foo)

File b.py:

from a import foo, Foo, set_foo

def tfunc():
    print('Old foo', foo)
    new_foo = Foo('third', 'fourth')
    set_foo(new_foo)
    print('New foo', foo)
    print(foo == new_foo)

tfunc()

When I run the program I get these results:

>python b.py
Old foo Foo(s1="first", s2="second")
Setting foo Foo(s1="third", s2="fourth")
New foo Foo(s1="first", s2="second")
False

Why is foo not getting set to the new value in the function tfunc?