© 1995-2011 | Anne Dawson All Rights Reserved.

Sunday 28th March 2010, 7:28 PT, AD

Python's + Operator - How to use with strings and numbers


The plus operator (+) in Python is an operator which has two operands.

For example, in the expression:

2  +  3

the   +   is the operator
and   2   is an operand and   3   is an operand.

In Python, there are some rules you need to understand about the + operator and its operands:

1)   If on the left of the + sign is a string, then on the right of the + sign must also be a string.
     According to rule #1, the following line of Python is OK:  
      
     print ( "2010 Year Of The "   +   "Tiger" )
    
     According to rule #1, the following line of Python is ***NOT*** OK:
      
     print ( 2010  +  "Year Of The Tiger" )


2)   If on the left of the + sign is a number, then on the right of the + sign must be a number.
     According to rule #2, the following line of Python is OK:
      
     print ( 2 + 3 )
    
     According to rule #2, the following line of Python is ***NOT*** OK:
      
     print ( 2  +  "3" )

     Explanation: in the line above, 2 is a number and "3" is a string.


and according to the rules, this is OK:

10 + int("3")



in the line above, the string "3" is converted to the integer (whole number) 3, 
and then the integer 3 is added to the integer 10 to make the value 13.

Question 1:  What would be the output when this Python line runs:

print ( 10 + int("5"))

Answer: 15

Question 2:  What would be the output when this Python line runs:

print ( str(10) + "5")

Answer: 105






Valid XHTML 1.0!

Valid CSS!