Default argument

Default arguments in Python functions allow you to specify values for arguments that will be used if no value is passed during the function call. This feature can make your functions more flexible and easier to use, as it provides default behaviors for cases where specific details aren't necessary.

Here’s how you define and use default arguments:

Defining a Function with Default Arguments: When defining a function, after the name of a parameter, you can assign a default value to it using the equals sign =. The parameters with default values must come after the parameters without default values in the function definition.

Calling a Function with Default Arguments: When calling a function that includes default arguments, you can omit those arguments, and the function will use the default values. If you provide values for these arguments when calling the function, the provided values will override the default ones.

Example of a Function with a Default Argument

Let's define a simple function that greets a user. The function will have one required argument (the name of the user) and one default argument (the greeting message).

def greet(name, message="Hello"):
   """Greet a user with a given message. If no message is provided, 'Hello' is used."""
   return f"{message}, {name}!"
# Using the function with the default argument
print(greet("Alice"))  # Output: Hello, Alice!
# Overriding the default argument
print(greet("Alice", "Good morning"))  # Output: Good morning, Alice!

In this example, message has a default value of "Hello". If greet is called with only the name argument, message will automatically be "Hello". However, you can also explicitly provide a different message when calling greet, which will override the default value.

Points to Remember

• Default arguments are evaluated only once when the function is defined, not each time the function is called. This is particularly important to remember when using mutable types (like lists or dictionaries) as default arguments.
• Parameters with default values must be defined after parameters without default values in the function’s parameter list to avoid syntax errors.