def f():
    s = 'foo'
    loc = locals()

    loc['s'] = 'bar'
    print(s)

    loc['z'] = 'baz'
    print(locals())

f()

I understand that the locals function returns a copy of the local namespace. That's why the value of s doesn't get modified in the actual local namespace. If that's the case, then why does an additional key-value pair to loc affect the actual local namespace?