Functions

This document explores Python functions, covering built-in and user-defined functions, their syntax, parameters, scope, and practical examples for code reuse and data processing. Readers will learn how to define, call, and document functions, and understand variable scope and common function patterns.

Introduction to Functions

Functions are reusable blocks of code that perform specific tasks. Python provides many built-in functions, and users can define their own to organize and simplify code.

Built-in Functions

Python includes built-in functions such as len, sum, and sorted:

Example:

1numbers = [10, 20, 5, 35]
2l = len(numbers)      # l = 4
3s = sum(numbers)      # s = 70
4sorted_numbers = sorted(numbers)  # [5, 10, 20, 35]

Methods vs Functions

• Functions operate independently and return new results.
• Methods are called on objects and may modify the object in place.

Example:

1album_ratings = [7, 8, 9, 6]
2sorted_ratings = sorted(album_ratings)  # Returns a new sorted list
3album_ratings.sort()                    # Modifies the original list

Defining User Functions

User-defined functions are created using the def keyword. Functions can accept parameters and return values.

Example:

1def add_one(a):
2    """Returns the input value plus one."""
3    b = a + 1
4    return b
5
6result = add_one(5)  # result = 6

Functions can have multiple parameters:

1def mult(x, y):
2    return x * y
3
4mult(2, 3)        # 6
5mult(10, 3.14)    # 31.4
6mult(2, "Hi")     # "HiHi"

Function Return Values

• If a function does not have a return statement, it returns None by default.
• The pass keyword is used for functions with no action.

Example:

1def no_work():
2    pass
3
4print(no_work())  # None

Function Documentation

Document functions using triple quotes at the start of the function body. The help() function displays this documentation.

Example:

1def add_one(a):
2    """Returns the input value plus one."""
3    return a + 1
4
5help(add_one)

Loops in Functions

Functions can include loops for processing data.

Example:

1def print_values(stuff):
2    for i, s in enumerate(stuff):
3        print(i, s)
4
5album_ratings = [7, 8, 9, 6]
6print_values(album_ratings)

Variadic Parameters

Functions can accept a variable number of arguments using *args.

Example:

1def print_names(*names):
2    for name in names:
3        print(name)
4
5print_names("Alice", "Bob", "Charlie")

Variable Scope

• Global variables are accessible throughout the program.
• Local variables exist only within the function scope.
• The global keyword can be used to modify global variables inside functions.

Example:

1date = 2017  # Global variable
2def thriller():
3    date = 1982  # Local variable
4    return date
5
6print(thriller())  # 1982
7print(date)        # 2017

Conclusion

Functions are essential for code reuse, organization, and data processing in Python. Understanding built-in and user-defined functions, parameters, return values, documentation, and scope enables efficient and maintainable programming.

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