The if and if-else Statements

15 min · Beginner

Programs make decisions based on runtime conditions. In Python, code blocks are defined strictly by indentation rather than curly braces.

The if statement and indentation

If statement is a line of code that runs an indented block only when its condition is True. When the condition is False, Python skips the block and moves on to the next line.

An if statement evaluates a condition. If the condition is truthy, the indented code block executes.

Python

cart_total = 750if cart_total >= 500:    print("Eligible for free shipping")

Example 1 · A block that is skipped

Python

order_total = 420if order_total >= 500:    print("Free shipping")print("Order placed")

Output

Order placed

What this code does

420 >= 500 is False, so the indented line is skipped.
print("Order placed") is not indented, so it belongs to no block and always runs.

PEP 8 specifies exactly 4 spaces per indentation level. Mixing tabs and spaces produces an IndentationError.

The if-else statement

If-else statement is an if with a second block after else. Exactly one of the two blocks runs: the if block when the condition is True, the else block when it is False.

Use else to provide an alternative execution path when the if condition evaluates to false.

Python

stock_count = 0if stock_count > 0:    print("In Stock")else:    print("Out of Stock")

A flow picture of if-else with cart_total = 750 and the condition cart_total >= 500. The condition is True, so the if block runs and prints Eligible for free shipping. The else block is skipped. Both paths then continue at the next line.

Example 2 · Approving a withdrawal

Python

1balance = 12002withdrawal = 5003
4if withdrawal <= balance:5    balance -= withdrawal6    print(f"Withdrawal approved. Remaining balance: {balance}")7else:8    print("Insufficient funds")

Output

Withdrawal approved. Remaining balance: 700

What this code does

Checks if withdrawal amount is within available balance.
Deducts amount and prints approved balance since 500 <= 1200.

Both the if and else lines end with a colon :. Exactly one of the two blocks will execute.

Idiomatic truthiness testing

Truthiness is how Python treats any value as True or False inside a condition. Values such as 0, an empty string and None count as False. Most other values count as True.

Instead of writing if len(name) > 0: or if is_admin == True:, write concise, idiomatic Python checks.

Python

username = "Anita"if username:    print(f"Welcome back, {username}")

Example 3 · Empty coupon field

Python

coupon = ""if coupon:    print(f"Coupon {coupon} applied")else:    print("No coupon applied")

Output

No coupon applied

What this code does

An empty string is falsy, so if coupon: is False.
Python runs the else block. With coupon = "SAVE10" the first line would run instead.

Because non-empty strings are truthy, if username: evaluates to True cleanly.

Next step

Check your understanding

8 quick questions

The if and if-else Statements

15 min · Beginner

Need help? Ask a tutor

Programs make decisions based on runtime conditions. In Python, code blocks are defined strictly by indentation rather than curly braces.

The if statement and indentation

If statement is a line of code that runs an indented block only when its condition is True. When the condition is False, Python skips the block and moves on to the next line.

An if statement evaluates a condition. If the condition is truthy, the indented code block executes.

Python

cart_total = 750if cart_total >= 500:    print("Eligible for free shipping")

Example 1 · A block that is skipped

Python

order_total = 420if order_total >= 500:    print("Free shipping")print("Order placed")

Output

Order placed

What this code does

420 >= 500 is False, so the indented line is skipped.
print("Order placed") is not indented, so it belongs to no block and always runs.

PEP 8 specifies exactly 4 spaces per indentation level. Mixing tabs and spaces produces an IndentationError.

The if-else statement

If-else statement is an if with a second block after else. Exactly one of the two blocks runs: the if block when the condition is True, the else block when it is False.

Use else to provide an alternative execution path when the if condition evaluates to false.

Python

stock_count = 0if stock_count > 0:    print("In Stock")else:    print("Out of Stock")

Example 2 · Approving a withdrawal

Python

1balance = 12002withdrawal = 5003
4if withdrawal <= balance:5    balance -= withdrawal6    print(f"Withdrawal approved. Remaining balance: {balance}")7else:8    print("Insufficient funds")

Output

Withdrawal approved. Remaining balance: 700

What this code does

Checks if withdrawal amount is within available balance.
Deducts amount and prints approved balance since 500 <= 1200.

Both the if and else lines end with a colon :. Exactly one of the two blocks will execute.

Idiomatic truthiness testing

Truthiness is how Python treats any value as True or False inside a condition. Values such as 0, an empty string and None count as False. Most other values count as True.

Instead of writing if len(name) > 0: or if is_admin == True:, write concise, idiomatic Python checks.

Python

username = "Anita"if username:    print(f"Welcome back, {username}")

Example 3 · Empty coupon field

Python

coupon = ""if coupon:    print(f"Coupon {coupon} applied")else:    print("No coupon applied")

Output

No coupon applied

What this code does

An empty string is falsy, so if coupon: is False.
Python runs the else block. With coupon = "SAVE10" the first line would run instead.

Because non-empty strings are truthy, if username: evaluates to True cleanly.

Next step

Check your understanding

8 quick questions