Decision Making Statements: If, If..else, Nested If..else and if-elif-else Ladder

Whether you're preparing for Python interviews, working on a Python project, or pursuing a Data Science or AI certification, understanding these conditional structures like `if`, `if-else`, `elif`, and `nested if` statements will help you write clear and efficient code.

 In this Python Tutorial, we will discuss how to make use of these statements and how they can help your coding and make it easier to maintain and read.

Types of decision-making statements in Python

There are four types of decision-making statements in the Python language those are

1. If statements in python
2. If else statement in python
3. Nested if else statement in Python
4. if-elif-else Ladder in Python

1. Read More: Explore all Python keywords, including if, else, and elif
2. Read More: Difference between For Loop and While Loop in Python

1. If statements in Python

• If statements in Python are conditional statements that only permit the execution of a code block if a predetermined condition is met. 
• The if keyword is followed by an indented block of statements that are executed if the condition is assessed and found to be true.
• If not, the code skips the if block.

Syntax of the If Statement in Python

if expression:
 statement(s)

Example of an If Statement in Python Editor

          num = 8
if num > 0:
  print("The number is positive.")

Output

The number is positive.

Explanation:

• Variable num is assigned the value 8.
• The condition num > 0 checks if the number is positive:
• Since 8 > 0 is True, the if block executes.
• It prints "The number is positive."

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2. If-else statement in Python

• If-else statements in Python are conditional statements along with the else block.
• If the condition in the if block evaluates to false, the else statement executes an alternate block of code. 
• 

Syntax of If-Else Statement in Python

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

Example of If If-Else Statement in Python

        num = 11
if num % 2 == 0:
  print("The number is even.")
else:
  print("The number is odd.")

Output

The number is odd.

Explanation:

• Variable num is assigned the value 11.
• The condition num%2 == 0 checks if the number is even:
• 11 % 2 equals 1, so the condition is False.
• The else block executes and prints "The number is odd."

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3. Nested if-else statement in Python

• Nesting an if-else statement refers to placing one or more if-else statements inside another if statement.
• Python enables the nesting of decision-making statements, which facilitates the development of more complex decision logic.

Syntax of Nested If-Else Statement in Python

if expression1:
 statement(s)
 if expression2:
   statement(s)
 elif expression3:
   statement(s)
 elif expression4:
   statement(s)
 else:
   statement(s)
else:
 statement(s)

Example of Nested If-Else Statement in Python Compiler

        num = 3
if num > 0:
  if num % 2 == 0:
    print("The number is positive and even.")
  else:
    print("The number is positive but odd.")
else:
  print("The number is not positive.")

Output

The number is positive but odd.

Explanation:

• Variable num is assigned the value 3.
• A nested if-else structure is used:
• First, it checks if num > 0 → True.
• Then, it checks if num % 2 == 0:
• Since 3 is not divisible by 2 → False.
• Executes the else block and prints "The number is positive but odd."

4. Python if-elif-else Ladder

• An if-elif-else ladder is an order of if statements connected by elif statements.
• This enables you to check for numerous conditions and run separate code blocks based on which condition is met.

Syntax of Python if-elif-else Ladder

if condition1: # code block 1
elif condition2:
 # code block 2
elif condition3:
 # code block 3
else:
 # default code block

Example of Python if-elif-else ladder

x = 11
if x == 2:
 print("x is equal to 2")
elif x == 3:
 print("x is equal to 3")
elif x == 4:
 print("x is equal to 4")
else:
 print("x is not equal to 2, 3, or 4")

Output

x is not equal to 2, 3, or 4

Explanation:

• Variable x is assigned the value 11.
• An if-elif-else ladder checks multiple conditions:
• If x == 2 → print "x is equal to 2"
• Else if x == 3 → print "x is equal to 3"
• Else if x == 4 → print "x is equal to 4"
• If none match → print "x is not equal to 2, 3, or 4"
• Since x is 11, none of the conditions match.

Shorthand if Statement

expression if condition else None

i = 21
if i > 15: print("i is greater than 15")

i is greater than 15

expression if condition else alternative_expression

  
age = 12
message = "You can vote" if age >= 18 else "You cannot vote yet"
print(message)

You cannot vote yet

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