Function body ¶

In Python, the function body is the code that runs when the function is called. It must be indented to show it belongs to the function.

Indentation Rules ¶

• Use exactly 4 spaces for indentation (not tabs).
• Every line of the function's code must be indented at the same level.
• Python uses indentation to understand what code belongs to the function.

def calculate_area(length, width):
    area = length * width    # Indented with 4 spaces
    return area             # Also indented with 4 spaces

def bad_indentation(x):
   print("Three spaces")    # ❌ Wrong: Only 3 spaces
     print("Five spaces")   # ❌ Wrong: 5 spaces
print("No spaces")          # ❌ Wrong: Not indented at all

Multiple Lines in Function Body ¶

All related code must be indented:

def calculate_total_price(price, tax_rate):
    # Everything indented belongs to the function
    subtotal = price
    tax = price * tax_rate
    total = subtotal + tax
    return total

Nested Indentation ¶

When you have loops or if-statements inside a function, they get an additional level of indentation:

def process_numbers(numbers):
    total = 0                           # First level: 4 spaces
    for number in numbers:              # First level: 4 spaces
        if number > 0:                  # Second level: 8 spaces
            total += number             # Third level: 12 spaces
    return total                        # Back to first level

The return statement ¶

A function can send back (or "return") a value to whoever called it using the return statement. Think of it like a function completing its task and reporting back with the result.

Basic Return Usage ¶

def calculate_area(length, width):
    area = length * width
    return area    # Sends the calculated area back

What Can Be Returned? ¶

Functions can return any type of data:

def get_pi():
    return 3.14159    # Returns a number

def get_greeting():
    return "Hello!"   # Returns a string

def get_coordinates():
    return [10, 20]   # Returns a list

def is_adult(age):
    return age >= 18  # Returns a boolean

Early Returns ¶

A function stops executing when it hits a return :

def check_temperature(temp):
    if temp > 100:
        return "Too hot!"          # Function ends here if temp > 100
    if temp < 0:
        return "Too cold!"         # Function ends here if temp < 0
    return "Just right!"           # Only reaches here if temp is 0-100

No Return Statement ¶

If a function doesn't have a return statement, it returns None by default:

def greet(name):
    print(f"Hello, {name}")    # Prints something but returns None

result = greet("Alice")
print(result)                  # Prints: None

Common Return Mistakes ¶

# ❌ Unreachable code after return
def bad_function():
    return "Hello"
    print("This never runs!")   # This line will never execute

# ❌ Forgetting to return
def calculate_sum(a, b):
    total = a + b              # Calculates but doesn't return!
    # Should be: return total

# ✅ Correct usage
def calculate_sum(a, b):
    total = a + b
    return total               # Returns the result