Python Functions

Function Parameters and Arguments

Python functions utilize parameters to receive input and arguments to provide that input during function calls. There’s a subtle but important distinction.

• Parameters: These are defined within the function’s definition. They act as placeholders for the values that will be passed in.

• Arguments: These are the actual values passed to the function when it’s called.

def greet(name, greeting="Hello"): # 'name' and 'greeting' are parameters
    print(f"{greeting}, {name}!")

greet("Alice") # "Alice" is an argument for 'name', "Hello" is the default argument for 'greeting'
greet("Bob", "Good morning") # "Bob" and "Good morning" are arguments

Types of Parameters:

• Positional Parameters: The order matters. Arguments are matched to parameters based on their position in the function call.

• Keyword Arguments: Arguments are explicitly assigned to parameters using the parameter name. Order doesn’t matter.

greet(greeting="Hi", name="Charlie") #Keyword Arguments

• Default Parameters: Parameters can have default values. If an argument isn’t provided for a parameter with a default, the default is used. Default parameters must come after non-default parameters in the function definition.

• Variable-Length Arguments (Arbitrary Arguments):

  • *args: Collects any number of positional arguments into a tuple.
  • **kwargs: Collects any number of keyword arguments into a dictionary.

def my_function(a, b, *args, **kwargs):
    print(f"a: {a}, b: {b}")
    print(f"args: {args}")
    print(f"kwargs: {kwargs}")

my_function(1, 2, 3, 4, 5, name="Alice", age=30)

Variable-Length Arguments

Argument Passing:

Python uses pass-by-object-reference. This means that when you pass a mutable object (like a list or dictionary) to a function, the function can modify the original object. If you pass an immutable object (like an integer or string), the original object is not modified within the function.

Pass-by-Object-Reference

Scope and Lifetime of Variables: Parameters have local scope within the function. Scope and Lifetime of Variables

Example illustrating mutability and immutability in argument passing:

def modify_list(my_list):
    my_list.append(4)

my_list = 1, 2, 3
modify_list(my_list)
print(my_list)  # Output: 1, 2, 3, 4  (List modified)


def modify_string(my_string):
    my_string += "!"

my_string = "hello"
modify_string(my_string)
print(my_string)  # Output: hello (String not modified in place)