Best Practice

• DRY: Dont Repeat Yourself

• Sample program to print numbers which are even and which are odd from 1 to n

max_value = int(input('Enter the max value'))

print(f'Even numbers from 1 to {max_value} are')
for index in range(1,max_value):
    if index%2 = 0:
        print(index)

print(f'Odd numbers from 1 to {max_value} are')
for index in range(1,max_value):
    if index%2 = 1:
        print(index)

• Mistake done at source will impact multiple places and you need to apply fix at multiple places/lines in your code.

• Solution: Rather than redundant code make it reusable.

• Basic programming construct to make code reusable is called as function.

Python functions

• function is a reusable code block
• syntax of function

def <nameofthefunction>(<args>):
    <function implementation>

• Example:

def add(number1, number2):
    result = number1 + number2
    print(f"{number1} + {number2} = {result}")

• Calling a function is just call by name of the function and pass arguments if any

def add(number1, number2):
    result = number1 + number2
    print(f"{number1} + {number2} = {result}")

add(3,5) # calling a function
add(number2= 5, number1= 3) # calling a function using named arguments.

Debugging Terms

• Step Into:
  • Step into will take the control inside the function
• Call Stack:
  • Stack consiting of trace information from where the code is called.

Adding Simple functions to our own POS

menu = """
Enter the number 
0 => View Products
1 => Add Product
2 => Update Product
3 => Delete Product
4 => Sell Items
5 => Report
6 => Exit
"""
# structure of dictionary will be
# {
#   '<code>' :  {
#        'name': '<product name>',
#        'quantity': <product quantity> 
#   }  
# }

# example:
#  products = {
#      'dell': { 'name': 'dell', 'cp': 30000, 'sp': 34000, 'quantity': 20, 'model': 'latitude'},
#      'hp': { 'name': 'hp', 'cp': 30000, 'sp': 34000, 'quantity': 20, 'model': 'elitebook'},
# }

products = {}

def ask_user_input(purpose):
    # This function asks for user input with custom message and returns the values
    user_input = input(f"Enter the {purpose} = ")
    return user_input

def does_product_exists(code):
    # returns whether the code exists or not
    return code in products.keys()



while True:
    choice = input(menu)
    if choice == '0':
        for code, product in products.items():
            print(f"{code} = {product}")
    elif choice == '1':
        code = input('Enter the product code name = ')
        if code in products:
            print(f'{code} already exists')
            continue
        product = {}
        product['name'] = ask_user_input('product name')
        product['model'] = ask_user_input('model')
        product['cp'] = float(ask_user_input('cost price'))
        product['sp'] = float(ask_user_input('selling price'))
        product['quantity'] = int(ask_user_input('available quantity'))
        products[code] = product
    elif choice == '2':
        code = ask_user_input('product code name')
        if code not in products.keys():
            print('Invalid code entered. Please check the code')
            continue
        quantity = int(ask_user_input('quantity to be added'))
        new_quantity = quantity + products[code]['quantity']
        products[code]['quantity'] = new_quantity
        print(f'quantity updated and new quantity is {new_quantity}')
    elif choice == '3':
        code = ask_user_input('product code name')
        if code not in products.keys():
            print('Invalid code entered. Please check the code')
            continue
        return_product = products.pop(code)
        print(f"{return_product} has been deleted")
    else:

        exit(0)

Function Types as of now

• We have two function types as of now
  • Functions which return value:
    • These functions have return statement

  def add(number1, number2):
     return (number1+number2)
  
  x = add(3,5)
  # x will have 8 
  
  
  

• Functions which donot
  • These functions don’t have return statement
  • But if you assign the function to variable as shown below, it will have None (variable not assigned to any memory)

def add(number1, number2):
    print(number1+number2)

x = add(3,5)
# x will have None

Functions with default arguments

• To understand this lets use Project Euler Problem 1

def project_euler_1(max_number, number1=3, number2=5):
    # This function has two default arguments number1 and number2
    # if you pass the value the value will be overwritten, if you dont pass the 
    # value, This functions takes default
    # example: project_euler_1(1000,5,3) => number1=> 5, number2 = 3
    # project_euler_1(1000) => number1 => 3, number2 => 5

    result = 0
    for index in range(1,max_number):
        is_divisible = (index%number1 == 0 or index%number2 ==0)
        if is_divisible:
            result = result+index
    return result

print(project_euler_1(1000))
    

Exercise: Create one module Projecteuler.py and create functions called as problem1, problem2 and so on

• Solve this

Project Euler 3 with Functions

def is_prime(number):
    # This function will return true if the number is prime, false otherwise
    is_prime_number = True
    for index in range(2,(number//2+1)):
        if number%index == 0:
            is_prime_number = False
            break
    return is_prime_number

def largest_prime_factor(number):
    # This function returns largest prime factor
    for index in range(number//2,2,-1):
        if number%index == 0 and is_prime(index):
            return index

print(largest_prime_factor(600851475143))