Python Function Basics: Creation, Parameters, and Usage

1. Creating a Function and Calling It

Define a simple function using def and call it to produce output.

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

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

2. Parameters

Functions can accept one or more parameters, which are specified in the definition and supplied when calling the function.

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

result = add(3, 5)
print(result)  # Output: 8

3. Parameter Count

Functions may have a fixed number of parameters or support variable numbers.

def multiply(x, y):
    return x * y

result = multiply(4, 5)
print(result)  # Output: 20

4. Arbitrary Positional Arguments (*args) *args collects any number of positional arguments into a tuple.

def sum_all(*args):
    total = 0
    for num in args:
        total += num
    return total

result = sum_all(1, 2, 3, 4, 5)
print(result)  # Output: 15

5. Keyword Arguments

Keyword arguments let you pass values using name=value pairs.

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

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

6. Arbitrary Keyword Arguments (**kwargs) **kwargs gathers any number of keyword arguments into a dictionary.

def print_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

print_info(name="Alice", age=30, city="New York")
# Output:
# name: Alice
# age: 30
# city: New York

7. Default Parameter Values

You can assign default values to parameters; they are used when the argument is omitted.

def describe_pet(pet_name, animal_type="dog"):
    print(f"I have a {animal_type} named {pet_name}.")

describe_pet("Willie")               # Output: I have a dog named Willie.
describe_pet("Harry", "hamster")  # Output: I have a hamster named Harry.

8. Passing a List as an Argument

A list can be passed to a function and iterated over.

def print_items(items):
    for item in items:
        print(item)

fruits = ["apple", "banana", "cherry"]
print_items(fruits)
# Output:
# apple
# banana
# cherry

9. Return Values

Functions can return one or multiple values using the return statement.

def get_person_info(name, age):
    return f"Name: {name}", f"Age: {age}"

person_info = get_person_info("Alice", 30)
print(person_info)  # Output: ('Name: Alice', 'Age: 30')

name, age = get_person_info("Alice", 30)
print(name)  # Output: Name: Alice
print(age)   # Output: Age: 30

10. The pass Statement pass acts as a placeholder where a statement is syntactically required but no action is needed.

def my_function():
    pass  # Placeholder for future code

my_function()  # Does nothing

11. Comprehensive Example

This example combines required arguments, *args, and **kwargs to demonstrate their joint usage.

def process_data(required_arg, *args, **kwargs):
    print(f"Required argument: {required_arg}")
    if args:
        print("Additional arguments:")
        for arg in args:
            print(arg)
    if kwargs:
        print("Keyword arguments:")
        for key, value in kwargs.items():
            print(f"{key}: {value}")

process_data("必需的参数", 1, 2, 3, name="Alice", age=30)
# Output:
# Required argument: 必需的参数
# Additional arguments:
# 1
# 2
# 3
# Keyword arguments:
# name: Alice
# age: 30