Python if … elif … else Statements

Learn to control the flow of a Python program using if, if...else and if...elseif statements. These statements are called conditional statements and help in writing boolean conditions that generally compare two variables or expressions.

a = 0

if a > 0:
    print("a is greater than 0")
elif a < 0:
    print("a is less than 0")
else:
    print("a is 0")

1. Using if

An “if statement” is written by using the if keyword.

a = 10
b = 20

if b > a:
  print("b is greater than a")      #Prints this message

1.1. Indentation

Python uses indentation to define the scope in the code. (Similar to curly brackets in Java). So be mindful of indentation while writing if else statements in Python.

1.2. Combining Multiple Expressions with Logical Operators

We can combine multiple expressions in the if statement using logical operators. Python provides two logical operators:

• and : Logical AND
• or : Logical OR

The following condition tests that b and c, both, are greater than a.

a = 10
b = 20
c = 30

if b > a and c > a:
  print("b and c are greater than a")   #Prints this message

1.3. Shorthand if

Whenever there is only a single statement to be executed inside the if block then shorthand if statement can be used. The statement can be put on the same line as the if statement. 

if b > a: print("b is greater than a")

2. Using if … else

The if statement is executed only if a certain condition is True. If the condition is False, then else statement is executed if provided in the program.

a = 100
b = 20

if b > a:
  print("b is greater than a")
else:
   print("b is smaller than a")     #Prints this message

We can write the shorthand if-else statement similar to the shorthand if statement we saw in the first section. Its syntax is:

statement_when_True if condition else statement_when_False

Let us rewrite the previous example in shorthand if-else statement.

a = 100
b = 20

print("b is greater than a") if (b > a) else print("b is smaller than a")  #Prints 'b is smaller than a'

3. Using elif

The elif statement is short form of else if statements in other programming languages such as Java. A Elif statement containing a conditional expression will be executed if its previous conditional expression is evaluated as False.

In this example, x is greater than y so the if statement will be False. So, the program will execute the elif statement which is True.

x = 100
y = 200
z = 300

if y < x:
	print('y is less than x')
elif y < z:
	print('y is less than z')  #Prints this message

4. Nested if .. else

We can have if statements inside another if statements, this is called nested if statements. We can compile these statements up to any level.

a = 20

if a > 10:
    print("a is greater than 10")	#Prints this message
    if a < 20:
        print("a is less than 20")
    else:
        print("a is equal to 20")    #Prints this message

5. Empty if

A Python program cannot have an empty if statement. If for any reason, you must provide an empty if statement then use the pass keyword.

x = 100
y = 200

if x < y:
	pass

Happy Learning !!