Various Function Return Methods

Functions are classified into the following 3 types based on their return method.

Exiting a Function Without Returning a Result

When a function is called without the return keyword, it returns None.

This is used when a function simply outputs a value using print but does not explicitly return a value.

Example of a Function Without a Return

# Function to print a message
def print_message(message):
    # Ends without return resulting in None
    print(message)

result = print_message("Hello")

# Prints None
print(result)

Returning a Value and Returning to the Call Location

When a value is specified after the return keyword, that value is returned.

The flow of the code returns to the calling location along with the returned result.

Example of a Function Returning a Value

def add(x, y):
    # Returns calculation result to the call location of add function
    return x + y

# 3 + 5 = 8
result = add(3, 5)
print(result)

Exiting a Function Without Returning a Value

Using only the return keyword, a function stops execution and returns None.

This method is useful when you want to immediately terminate the function execution under specific conditions.

Exiting Function When num is Negative

def check_number(num):
    if num < 0:
        return
    print("It is a positive number.")

result1 = check_number(-1)
print(result1)  # None

result2 = check_number(1)
print(result2)  # It is a positive number.

In the example above, when num is negative, the function is immediately terminated using only the return keyword, resulting in None.

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