“num - 1” vs “num -= 1”

Question

In line 4 why do we have to add \"=\" after \"-\" ?

num = 5
if num > 2:
    print(num)
    num -= 1
print(num)

Answer 1

-= is an operator. This operator is equals to subtraction.

num -= 1 means is num = num - 1

It is used to subtraction from the itself with given value in right side.