How to set default arguments in Python functions?

Default Arguments in Python Functions

In Python, you can define default arguments for a function, which allows the function to be called with fewer arguments than it is defined with. When a function is called with fewer arguments than it expects, the default values are used for the missing arguments.

Understanding Default Arguments

Let's consider a simple example to understand how default arguments work in Python:

def greet(name, greeting="Hello"):
    print(f"{greeting}, {name}!")

greet("Alice")  # Output: Hello, Alice!
greet("Bob", "Hi")  # Output: Hi, Bob!

In the above example, the greet() function has two parameters: name and greeting. The greeting parameter has a default value of "Hello". When the function is called with only one argument (greet("Alice")), the default value of "Hello" is used for the greeting parameter. When the function is called with two arguments (greet("Bob", "Hi")), the second argument overrides the default value.

Defining Default Arguments

To define default arguments in a Python function, you simply need to assign a value to the parameter in the function definition. The syntax looks like this:

def function_name(param1, param2=default_value, param3=default_value):
    # function body
    pass

Here, param2 and param3 have default values assigned to them. When the function is called, if these arguments are not provided, the default values will be used.

It's important to note that default arguments are evaluated once when the function is defined, not each time the function is called. This means that if the default value is a mutable object (like a list or a dictionary), the same object will be used for all function calls, which can lead to unexpected behavior. To avoid this, it's recommended to use immutable objects (like None or 0) as default values, or to use a different approach, such as using None as the default and then checking for it inside the function.

Mermaid Diagram: Default Arguments in Python Functions

This diagram illustrates the process of defining and using default arguments in Python functions. The function definition specifies the parameters and their default values, and when the function is called, the default values are used for any missing arguments.

Real-World Example: Calculating the Area of a Rectangle

Suppose you have a function to calculate the area of a rectangle. You can use default arguments to make the function more flexible:

def calculate_area(length, width=1):
    """
    Calculate the area of a rectangle.

    Args:
        length (float): The length of the rectangle.
        width (float, optional): The width of the rectangle. Defaults to 1.

    Returns:
        float: The area of the rectangle.
    """
    return length * width

# Examples
print(calculate_area(5))      # Output: 5.0
print(calculate_area(3, 4))  # Output: 12.0

In this example, the calculate_area() function has a default argument for the width parameter. If the width is not provided when the function is called, it defaults to 1, allowing the function to be used to calculate the area of a square (where the length and width are the same) or a rectangle (where the length and width are different).

Using default arguments in this way makes the function more versatile and easier to use, as the caller doesn't always need to provide all the required arguments.