If statements

In Python you can define conditional statements, known as if-statements. A block of code is executed if certain conditions are met.

If statements

Consider this application, it executes either the first or second code depending on the value of x.

#!/usr/bin/python
x = 3
if x > 10:
    print("x smaller than 10")
else:
    print("x is bigger than 10 or equal")

Want more practice on this without setting anything up? PyChallenge has graded loop and condition exercises that run in the browser, and the error message tells you what went wrong.

If you set x to be larger than 10, it will execute the second code block.   We use indentation (4 spaces) to define the blocks.

A little game: A variable may not always be defined by the user, consider this little game:

age = 24
print "Guess my age, you have 1 chances!"
guess = int(raw_input("Guess: "))
if guess != age:
    print("Wrong!")
else:
    print("Correct")

Conditional operators

A word on conditional operators Do not confuse the assignment operator (=) with the equals operator (==).

Nesting

The most straightforward way to do multiple conditions is nesting:

a = 12
b = 33
if a > 10:
    if b > 20:
        print("Good")

This can quickly become difficult to read, consider combining 4 or 6 conditions.  Luckily Python has a solution for this, we can combine conditions using the and keyword.

guess = 24
if guess > 10 and guess < 20:
    print("In range")
else:
    print("Out of range")

Sometimes you may want to use the or operator.

Operator	Description
!=	not equal
==	equals
>	greater than
<	smaller than