What is an example of a user-defined function in Python?

You can define your own functions using the def keyword. Here’s a simple example of a user-defined function that calculates the square of a number:

def square(number):
    """This function returns the square of the given number."""
    return number ** 2

Let’s break down the components of this function:

  • def: This keyword is used to start the definition of a function.
  • square: This is the name of the function. You can choose any valid name for your function.
  • (number): This is the function’s parameter list. Here, we have a single parameter named number, which is the input to the function.
  • """This function returns the square of the given number.""": This is called a docstring. It is a multi-line string that provides a brief description of what the function does. It’s good practice to include docstrings in your functions to explain their purpose and usage.
  • return number ** 2: This is the body of the function. It calculates the square of the number parameter using the ** exponentiation operator and returns the result.

After defining the function, you can call it by passing an argument to it. For example:

result = square(5)
print(result)  # Output: 25

In this example, the square() function is called with the argument 5, and it returns 25, which is the square of 5.

How do you write a user-defined function?

To write a user-defined function in Python, you need to follow these steps:

  1. Use the def keyword followed by the function name to start the function definition.
  2. Define the function parameters within parentheses (). Parameters are inputs that the function can accept. You can have zero or more parameters.
  3. Add a colon : at the end of the function definition line.
  4. Indent the function body with four spaces (or a tab). This is important as Python uses indentation to determine the scope of the function.
  5. Write the code statements that make up the body of the function.
  6. Optionally, include a return statement to specify the value the function should return. If there’s no return statement, the function returns None by default.

Here’s a more general template for writing a user-defined function:

def function_name(parameter1, parameter2, ...):
    """Optional docstring: description of the function."""
    # Function body: code statements that perform some operations.
    # Optionally, use the 'return' statement to provide a result.
    return result

Let’s see an example of a simple user-defined function that adds two numbers:

def add_numbers(a, b):
    """This function adds two numbers and returns the result."""
    result = a + b
    return result

You can call this function by passing two numbers as arguments:

sum_result = add_numbers(3, 5)
print(sum_result)  # Output: 8

Remember that you can have user-defined functions with zero or more parameters, and they can return different types of values or even no values (using return without any expression).

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  • Yaryna Ostapchuk

    I am an enthusiastic learner and aspiring Python developer with expertise in Django and Flask. I pursued my education at Ivan Franko Lviv University, specializing in the Faculty of Physics. My skills encompass Python programming, backend development, and working with databases. I am well-versed in various computer software, including Ubuntu, Linux, MaximDL, LabView, C/C++, and Python, among others.

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