Introduction to Operators

A biologist, a physicist, and a mathematician are all eating on the patio of a restaurant. Across the street, they see two people walk into a building, and a few moments later three people walk out.

The biologist says, “Oh, they must have reproduced.”

The physicist remarks, “There must have been some type of statistical error.”

All are quiet for a long while before the mathematician says, “You know, if one more person walks into that building it will be empty.”

We have already come across the assignment operator ( = ) in the previous section, where we used it to assign values to a variable name. Let us do the same here:

 > entered = 2
 > walked_out = 3

Now we can use a couple of arithmetic operators to see what’s going on in the mathematician’s mind:

 > remaining = entered - walked_out
 > remaining
=> -1
 > remaining + 1
=> 0

Here is a full list of the Python arithmetic operators:

Operator	Name	Description	Example
+	Addition	…	…
-	Subtraction	…	…
*	Multiplication	…	…
/	Division	…	…
%	Modulus	…	…
**	Exponent	…	…
//	Floor Division	…	…

You can actually use a Python console as a calculator (try it!):

 > 2/3
=> 0.6666666666666666
 > 2//3
=> 0
 > 2**3
=> 8
 > 2 + 3/5
=> 2.6
 > (2 + 3)/5
=> 1.0
 > 2*3 + 2**3
=> 14 

Some of the above operators also work on non numeric data types:

 > password = 'dolph!ns'              # this is not my password and you should never store passwords in code
 > a_single_space = ' '
 > my_favorite_number = '111'         # again, note the quotes, this is different from 111 (without quotes), more on this in the next section
 > a_slightly_more_secure_password = password + a_single_space + my_favorite_number
 > a_slightly_more_secure_password    # What do you think the output will be?

Expand to reveal the output

 # Well, it would be the same as:
 > 'dolph!ns' + ' ' + '111'
=> 'dolp!ns 111'

# FIXME: Organize this.
#        Do data types and operators belong together?
#        How do we explain string concatenation?

Previous (Variables)	Home	Next (Types)