Source: 📖 Effective Python item 11
Values can be assigned to a slice with the assignment operator =. A copy is not created in this case; the original list is changed in place.
my_list = [1, 2, 3, 4, 5, 6]
my_list[2:4] = ['a', 'b']
print(my_list)
>>>
[1, 2, 'a', 'b', 5, 6]
Unlike in multiple assignment unpacking, both sides of the = assignment operator do not need to be the same length—the list will grow or shrink to adapt to the length of the new values.
my_list = [1, 2, 3, 4, 5, 6]
my_list[2:5] = ['a', 'b'] # list shrinks
print(my_list)
>>>
[1, 2, a, b, 6]
my_list = [1, 2, 3, 4, 5, 6]
my_list[2:3] = ['a', 'b'] # list grows
print(my_list)
>>>
[1, 2, 'a', 'b', 4, 5 6]