What is the meaning of "+="

Answer 1

Adding first the right element with left element and then assigning the same value to left element
E. G. a += b means
a = a + b

Answer 2

Already answered so this is just for visitors who want to read further:

Python inplace (in-place) operators:
http://www.geeksforgeeks.org/inplace-operators-python-set-1iadd-isub-iconcat/

Answer 3

thanks bro