• With branching using If, Elif, or Else statements I can control the execution of the code.
  • The code block will only be executed if the condition is True.
if condition:
    run this code
elif other_condition_occured:
    run this code over here not the one above
else:
    run this code for anything else that don't meet the conditions above
  • Example:
option = input("Choose 1 to Multiply numbers, Choose 2 to Divide: ")

num1 = int(input("Enter the first number --> "))
num2 = int(input("Enter the second number --> "))

if option == "1":
	print(f"{num1} multiplied by {num2} is {num1 * num2}")
elif option == "2":
	print(f"{num1} divided by {num2} is {num1 / num2}")
else:
	print("That's an invalid selection")

If elif

  • The usage of if, elif, and else in the code above works fine if the user choose either option 1 or 2, but it will still prompt the user to enter the first number even when the user entered something else other than 1 or 2 Invalid selection

  • To fix this I can use Nested If Statements

option = input("Choose 1 to Multiply numbers, Choose 2 to Divide: ")

if option == "1" or option == "2":
	num1 = int(input("Enter the first number --> "))
	num2 = int(input("Enter the second number --> "))
	if option == "1":
		print(f"{num1} multiplied by {num2} is {num1 * num2}")
	else:
		print(f"{num1} divided by {num2} is {num1 / num2}")
else:
	print("That's an invalid selection")

Nested if

  • Example:
user_choice = "1"
paid = True

if user_choice == "1" and paid:
	print("You chose option 1")
elif user_choice == "2":
    print("You chose option 2")
else:
    print("Invalid choice")

  • For if statement to be executed, user_choice and paid both have to be True if statement

  • When paid is changed to False the if statement will not be executed, it will go to check for the next statements and in this case it will run the else statement

user_choice = "1"
paid = False

if user_choice == "1" and paid:
    print("You chose option 1")
elif user_choice == "2":
    print("You chose option 2")
else:
    print("Invalid choice")

If statement false

  • Example:
raining = True

a = "Bring an umbrella"
b = "It's a sunny day!"

if not raining:
	print(a)
else:
	print(b)

  • This will execute the else statement because the if statement will check for the opposite value of raining variable. Using not

  • The code above can be simplified and written in one line using Ternary operators

raining = True
a = "Bring an umbrella"
b = "It's a sunny day!"  

print(a) if not raining else print(b)

print(b) if raining else print(a)

Ternary operator

  • See the Boolean Truth Table as reference Truth table