Creating a Python decorator to log function arguments and return value

Last update on April 21 2025 12:58:32 (UTC/GMT +8 hours)

1. Create a Decorator to Log Function Arguments and Return Value

Write a Python program to create a decorator that logs the arguments and return value of a function.

The decorator in this code logs the function name, arguments, and return value whenever the decorated function is called.

Sample Solution:

Python Code:

def decorator(func):
    def wrap(*args, **kwargs):
        # Log the function name and arguments
        print(f"Calling {func.__name__} with args: {args}, kwargs: {kwargs}")
        
        # Call the original function
        result = func(*args, **kwargs)
        
        # Log the return value
        print(f"{func.__name__} returned: {result}")
        
        # Return the result
        return result
    return wrap

# Example usage
@decorator
def multiply_numbers(x, y):
    return x * y

# Call the decorated function
result = multiply_numbers(10, 20)
print("Result:", result)

Sample Output:

Calling multiply_numbers with args: (10, 20), kwargs: {}
multiply_numbers returned: 200
Result: 200

Explanation:

In the above exercise -

The "decorator()" function is defined with a single parameter func, representing the function to be decorated.
Inside the decorator function, another function called "wrap()" is defined. This "wrap()" function serves as a wrapper function that adds extra functionality to the original function.
The "wrap()" function accepts any number of positional and keyword arguments (*args and **kwargs), allowing it to handle functions with varying arguments.
The wrapper function first logs the function name and its arguments using formatted string literals (f"...").
The original function is then called using func(*args, **kwargs), and the result is stored in the result variable.
The wrapper function logs the return value after calling the original function.
Finally, the wrapper function returns the result.

The "@decorator" syntax is used to apply the "decorator" to the "multiply_numbers()" function, indicating that it should be decorated with the functionality provided by the "decorator()" function.

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python decorator that logs the function name, its input parameters, and output to the console using print().
Write a Python decorator that writes the function’s arguments and return value to a file each time the function is called.
Write a Python decorator that stores the log of a function call in a global list for later analysis.
Write a Python decorator that conditionally logs calls based on a debug flag passed as an argument to the decorator.

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