6.6 Keyword arguments

Python functions offer versatile ways to pass arguments. Positional arguments rely on order, while keyword arguments use parameter names. This flexibility allows for clearer, more readable code and easier function calls with multiple parameters.

Default parameter values provide convenience and flexibility in function calls. They allow optional parameters and can be overridden when needed. Keyword arguments enhance readability, flexibility, and maintainability, making complex function calls more manageable and intuitive.

Function Arguments in Python

Positional vs keyword arguments

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• Positional arguments passed to a function based on their position or order
  • Order of arguments in function call must match order of parameters in function definition (parameter order)

  • def greet(name, age):

    calling

    greet("Alice", 25)

    assigns

    "Alice"

    to

    name

    and

    25

    to

    age

• Keyword arguments passed to a function using parameter names along with corresponding values
  • Order of arguments doesn't matter as long as parameter names are specified

  • def greet(name, age):

    calling

    greet(age=25, name="Alice")

    achieves same result as

    greet("Alice", 25)

• Mixing positional and keyword arguments allowed
  • Positional arguments must come before keyword arguments

  • greet("Alice", age=25)

    is valid, but

    greet(name="Alice", 25)

    is not

Default parameter values

• Specify default value for a parameter in function definition
  • If argument not provided for that parameter when function is called, default value is used

  • def greet(name, age=18):

    if

    age

    not provided when calling

    greet()

    , it defaults to

    18

• Calling functions with default parameter values
  • Omit arguments for parameters with default values (

    greet("Alice")

    uses default value of

    18

    for

    age

    )
  • Override default values by providing arguments (

    greet("Alice", 25)

    overrides default

    age

    with

    25

    )
  • Use keyword arguments to specify only parameters you want to override (

    greet("Alice", age=25)

    overrides default

    age

    while keeping positional argument for

    name

    )
• Default values create optional parameters in the function definition

Benefits of keyword arguments

• Improved readability
  • Make purpose of each argument clear in function call

  • draw_rectangle(width=10, height=5)

    more readable than

    draw_rectangle(10, 5)

  • Especially useful when function has many parameters or purpose of each argument not immediately clear
• Flexibility in argument order
  • Allow specifying arguments in any order

  • draw_rectangle(height=5, width=10)

    equivalent to

    draw_rectangle(width=10, height=5)

  • Helpful when function has many optional parameters
• Selective argument overriding
  • Override only specific default values

  • def create_user(name, age=18, email=None):

    can call

    create_user("Alice", email="alice@example.com")

    to override only

    email

    parameter while keeping default

    age

• Improved maintainability
  • If function definition changes to add, remove, or reorder parameters, existing function calls with keyword arguments may not need to be updated
  • Makes code more maintainable and less prone to errors when refactoring

Function Definition and Calling

• Function definition establishes the parameters and their order
• Function call involves argument passing to match the defined parameters
• The relationship between definition and call determines how arguments are interpreted