全局可变与不可变

Question

Is the following a correct understanding of global on mutable vs immutable objects?

immutable1 = 'abc'
immutable2 = '123'
mutable = {}

def change():    
    mutable['CHANGED'] = 'CHANGED' # this will change the global variable mutable
    global immutable1
    immutable1 = 'abc-CHANGED' # this will change the global variable immutable1 because global has been called
    immutable2 = '123-CHANGED' # this will not change the global immutable2 variable, because it's immutable and global has not bee declared

Is the only usage of global to modify a global immutable variable, or can it ever be used in other situations?

Another example:

>>> m={}
>>> i='a'
>>> 
>>> def change():
...     m['a'] = i
...     i = 'b'
... 
>>> print(m,i)
{} a
>>> change()
UnboundLocalError: local variable 'i' referenced before assignment

Answer 1

global has nothing to do with mutability. It changes the scope of a name , whether the global refers to a mutable or immutable object, so that you can assign a different value to the name.

When assigning to a global name, the old value may or may not have been mutable, and the new value can be either as well.

d = {}
e = 6

def change():
    global d, e
    d = 3
    e = []