Functions in Python

Ahmed Moustafa

Functions

• Functions are reusable blocks of code that perform a specific task
• They can take input parameters and return output values
• Functions are essential in modular programming, as they help organize code and make it more readable

Defining a Function

• To define a function in Python, use the keyword def followed by the function name and input parameters in parentheses
• The function body is indented below the header line
• Use the keyword return to specify the output value(s) of the function

def add_numbers(x, y):
    result = x + y
    return result

Calling a Function

To call a function, use its name followed by input values in parentheses The function returns the output value(s), which can be stored in a variable or used directly

sum = add_numbers(2, 3)
print(sum)

5

Default Parameter Values

• Functions can have default values for input parameters, which are used when no value is provided
• Default values are specified in the function header

def greet(name, greeting = "Hello"):
    print(greeting + ", " + name)

greet("Alice")

Hello, Alice

greet("Bob", "Hi")

Hi, Bob

Variable-Length Arguments

• Variable-length arguments allow a function to accept any number of input arguments
• They are useful when the number of input arguments is unknown or can vary

def add_numbers(*args):
    result = 0
    for num in args:
        result += num
    return result

add_numbers

<function __main__.add_numbers(*args)>

add_numbers(1, 2, 3)

6

add_numbers(1, 2, 3, 4, 5)

15

Function Annotation

def add_numbers(*args):
    
    """
    Computes the sum of n numbers
    
    Parameters:
    args: A tuple of numbers
    
    Returns:
    int: The sum
    """        
    
    result = 0
    for num in args:
        result += num
    return result

help(add_numbers)

Help on function add_numbers in module __main__:

add_numbers(*args)
    Computes the sum of n numbers
    
    Parameters:
    args: A tuple of numbers
    
    Returns:
    int: The sum

Lambda Functions

• Lambda functions are anonymous functions that can be defined inline and used immediately
• They are useful for simple tasks that don't require a named function
• Lambda functions can only have one expression

double = lambda x: x * 2
print(double(3))

6

Recursion

• Recursion is a technique where a function calls itself
• It is useful for solving problems that can be broken down into smaller subproblems

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n-1)

print(factorial(5))

120

Global vs Local Variables

• Global variables are defined outside of any function and can be accessed from anywhere in the program
• Local variables are defined inside a function and can only be accessed within that function

global_var = 10

def my_func():
    local_var = 20
    print(global_var)
    print(local_var)

my_func()

10
20

print(global_var)

10

print(local_var)

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Cell In[15], line 1
----> 1 print(local_var)

NameError: name 'local_var' is not defined

Error Handling

• Error handling is the process of detecting and responding to errors in a program
• Python has a try-except block for handling exceptions that might occur in a function

def divide(x, y):
    try:
        result = x / y
    except ZeroDivisionError:
        print("Error: division by zero")
    else:
        return result

print(divide(10, 5))

2.0

print(divide(10, 0))

Error: division by zero
None

Conclusion

• Functions are a fundamental concept in Python programming
• They help to modularize code, making it more organized and easier to maintain
• There are many types of functions and techniques for working with them
• Understanding these concepts can help to write more efficient, flexible, and readable code