Table of Contants- Function Definition

• Function Concepts
• Three Forms of Function Definision
• Return Values in Functions
• Function Parameters

Function Definition

def register_user():
    # Registration functionality
    print('Registration function')
    user_input = input('Enter your username: ')
    password_input = input('Enter your password: ')
    with open('user_info.txt','a',encoding='utf8') as file:
        if ':' in user_input or ':' in password_input:
            print('Invalid input, cannot contain ":"')
        else:
            file.write(f'{user_input}:{password_input}')
            print('Saved successfully')


# Login functionality
# print('Login function')
# with open('user_info.txt','r',encoding='utf8') as file:
#     data = file.read()
#     user_data_list = data.split(':')
# username,password = user_data_list[0],user_data_list[1]
# username_input = input('Enter your username: ')
# password_input = input('Enter your password: ')
#
# if username == username_input and password == password_input:
#     print('Login successful')
# else:
#     print('Login failed')

# Above only defines a function, creating a tool (syntax is checked during definition phase but code isn't executed).
# To execute the function, call it directly.

register_user()

Function Concepts

# Function: In mathematics, a function maps inputs to outputs - this concept has no relation to mathematical functions.

# Sewer system --> Clearing sewers --> Get a tool (buy one) --> Convenient, ready to use
# A function is like this tool --> performs a specific task
# Functions separate tools, not reducing code volume
# Guess the number game code
def higher_number():
    num1 = 10
    num2 = 20
    if num1 > num2:
        print(num1)
    else:
        print(num2)
def calculate_sum():
    num1 = 10
    num2 = 20
    print(num1+num2)
# Use the functions
higher_number()
calculate_sum()

# Function syntax
'''
# Create a tool, not yet used
def function_name(tool_name): --> follows variable naming rules
    <function implementation>
# Call function when needed
function_name()
'''
# Functions separate functionalities and allow calling when required

Three Forms of Function Definition

# Empty function
def register_user():
    # TODO: Registration functionality, temporarily not implemented
    pass    # Placeholder for empty function

# Parameterized function (function with parameters)
def compare_numbers(a,b):
    if a > b:
        print(a)
    else:
        print(b)
compare_numbers(30,40)  # Must provide arguments when calling
# When using a flashlight, you don't modify internal components, just activate it (pass an argument)

# Parameterless function
def simple_function():
    print(1)
simple_function()

Return Values in Funnctions

# def add_numbers(a,b):
    # Various logic
#     return a + b    # Function return value
# result = add_numbers(10,20)
# print(result)


# def add_numbers(a,b):
#     # Various logic
#     print(a+b)
#     return a + b    # Function return value; terminates function execution
#     print(1)
# print(2)
# result = add_numbers(10,20)
# print(result)

# def add_numbers(a,b):
#     # Various logic
#     print(a+b)
#     # return a + b    # Function return value; terminates function execution
#     print(1)
# print(2)
# result = add_numbers(10,20)    # If no return, assigning function call result to variable defaults to None
# print(result)

def add_numbers(a,b):
    # return(a,b,a+b) # Return can return any data type
    return a,b,a+b  # Return can return any data type, multiple values without parentheses default to tuple
result = add_numbers(1,2)
print(result)
a,b,c = add_numbers(1,2)    # Unpacking
print(a,b,c)

Function Parameters

# def add_numbers(a,b):
    # Various logic
#     return a + b    # Function return value
# result = add_numbers(10,20)
# print(result)


# def add_numbers(a,b):
#     # Various logic
#     print(a+b)
#     return a + b    # Function return value; terminates function execution
#     print(1)
# print(2)
# result = add_numbers(10,20)
# print(result)

# def add_numbers(a,b):
#     # Various logic
#     print(a+b)
#     # return a + b    # Function return value; terminates function execution
#     print(1)
# print(2)
# result = add_numbers(10,20)    # If no return, assigning function call result to variable defaults to None
# print(result)

def add_numbers(a,b):
    # return(a,b,a+b) # Return can return any data type
    return a,b,a+b  # Return can return any data type, multiple values without parentheses default to tuple
result = add_numbers(1,2)
print(result)
a,b,c = add_numbers(1,2)    # Unpacking
print(a,b,c)