Let me illustrate onpon4's statement:
Python 3
---------
num = input()
# input a number, let us say 5
sum = num + num
Print (sum)
55 # concatenation of two strings '5' and '5'
Python 2
---------
num = input()
# input a number, let us say 5
sum = num + num
Print (sum)
10 # sum of two integers 5 and 5
To get this result of 10 using Python 3 you can do the following:
Python 3
---------
num = int( input() ) # convert input to an integer
# input a number, let us say 5
sum = num + num
Print (sum)
10 # sum of two integers 5 and 5
Conclusion: In Python 2 the result of input() is an int while in Python 3 the
result of input() is a string.
