Functions

Defining Functions

A function is a block of reusable code that performs a specific task.

In Python, you define a function using the def keyword, followed by the function name and parentheses enclosing any parameters.

The function body is indented.

Syntax:

def function_name(parameters):
    # Block of code

Example:

def greet(name):
    print('Hello, ' + name + '!')

Calling the Function:

greet('Alice')  # Output: Hello, Alice!
greet('Bob')    # Output: Hello, Bob!

Return Statement

The return statement is used to send a result back from the function to the caller.

After the return statement is executed, the function exits and the control is returned to the place where the function was called.

Syntax:

def function_name(parameters):
    # Block of code
    return value

Example:

def add(a, b):
    result = a + b
    return result

Calling the Function:

sum = add(3, 4)
print(sum)  # Output: 7

Lambda Functions

A lambda function is a small, anonymous function defined using the lambda keyword.

It can take any number of arguments but can only have one expression.

The expression is evaluated and returned when the lambda function is called.

Syntax:

lambda parameters: expression

Example:

multiply = lambda x, y: x * y

Calling the lambda:

result = multiply(3, 4)
print(result)  # Output: 12

Default Arguments

You can assign default values to parameters when defining a function.

These default values will be used if no argument is passed for those parameters when the function is called.

Example:

def greet(name='Guest'):
    print('Hello, ' + name + '!')

Calling the Function:

greet()         # Output: Hello, Guest!
greet('Alice')  # Output: Hello, Alice!

Keyword Arguments

You can also specify the values of arguments by their parameter names when calling a function.

Example:

def introduce(name, age):
    print('My name is ' + name + ' and I am ' + str(age) + '.')

Calling the Function:

introduce(age=24, name='Daniel')

Output:

My name is Daniel and I am 24.

Arbitrary Arguments

*args allows you to pass a variable number of non-keyword arguments (positional arguments) to a function.

**kwargs allows you to pass a variable number of keyword arguments to a function.

Example:

def my_function(name, *args, age=None, **kwargs):
    print(name)
    print(args)
    print(age)
    print(kwargs)

Calling the Function:

my_function('Daniel', 1, 2, 3, 4, height=182)

Output:

Daniel
(1, 2, 3, 4)
None
{'height': 182}

Docstrings

A docstring is a special type of string that is used to document a function.

It is placed immediately after the function definition and can be accessed using the help() function or .__doc__.

Example:

def greet(name):
    """This function greets the person passed in as a parameter."""
    print('Hello, ' + name + '!')

Calling the Function:

print(greet.__doc__)

Output:

This function greets the person passed in as a parameter.

Returning Multiple Values

A function in Python can return multiple values.

These values are returned as a tuple, which is implicitly created when multiple values are returned. You can then unpack these values into separate variables when calling the function.

Example:

def get_coordinates():
    return 4, 5, 'Madrid'

Calling the Function:

x, y, city = get_coordinates()
print(x, y, city)

Output:

4 5 Madrid

Last modified: 17 March 2025