if condtion

An else statement can be combined with an if statement. An else statement contains the block of code that executes if the conditional expression in the if statement resolves to 0 or a false value.
The else statement is an optional statement and there could be at most only one else statement following if .

Syntax:

The syntax of the if...else statement is:

if expression:
   statement(s)
else:
   statement(s)

Flow Diagram:

Example:

#!/usr/bin/python

var1 = 100
if var1:
   print "1 - Got a true expression value"
   print var1
else:
   print "1 - Got a false expression value"
   print var1

var2 = 0
if var2:
   print "2 - Got a true expression value"
   print var2
else:
   print "2 - Got a false expression value"
   print var2

print "Good bye!"

When the above code is executed, it produces the following result:

1 - Got a true expression value
100
2 - Got a false expression value
0
Good bye!

The elif Statement

The elif statement allows you to check multiple expressions for truth value and execute a block of code as soon as one of the conditions evaluates to true.
Like the else, the elif statement is optional. However, unlike else, for which there can be at most one statement, there can be an arbitrary number of elif statements following an if.
The syntax of the if...elif statement is:

if expression1:
   statement(s)
elif expression2:
   statement(s)
elif expression3:
   statement(s)
else:
   statement(s)

Core Python does not provide switch or case statements as in other languages, but we can use if..elif...statements to simulate switch case as follows:

Example:

#!/usr/bin/python

var = 100
if var == 200:
   print "1 - Got a true expression value"
   print var
elif var == 150:
   print "2 - Got a true expression value"
   print var
elif var == 100:
   print "3 - Got a true expression value"
   print var
else:
   print "4 - Got a false expression value"
   print var

print "Good bye!"

When the above code is executed, it produces the following result:

3 - Got a true expression value
100
Good bye!