Key Differences Between if-else & if-elif-else:

Featureif-elseif-elif-else
Number of conditionsOnly two conditionsMultiple conditions
Execution FlowOne of the two blocks always executesChecks multiple conditions sequentially
EfficiencySimple and directMore flexible but stops after the first match
Use CaseBinary choices (Yes/No, True/False)Multiple possible values or categories

Multiway if-elif-else statement:

  • Represents an if statement that considers each condition until one evaluates to True or they all evaluate to False. When a condition evaluates to True the corresponding action is performed and the control skips to the end of the entire selection statement.
  • If no condition evaluates to True, then the action after the trailing else is performed.
  • The syntax is as follows:
python
1if condition1:
2	# Code to execute if condition1 is True
3elif condition2:
4	# Code to execute if condition2 is True
5elif condition3:
6	# Code to execute if condition3 is True
7# More elif blocks can be added as needed
8else:
9	# Code to execute if none of the above conditions are True
  • Example: Let’s imagine we want to write a statement to determine and print the letter grade corresponding to an input numeric grade:
    • Prompt: Enter the numeric grade: 82
python
1number = int(input("Enter the numeric grade: "))
2
3if number > 89:
4    letter = "A"
5elif number > 79:
6    letter = "B"
7elif number > 69:
8    letter = "C"
9elif number > 59:
10    letter = "D"
11else:
12    letter = "F"
13print("The letter grade is, " + letter)

Output:

1The letter grade is, B

Testing Multiple Conditions:

  • Often, you’ll need to categorize items into different groups based on multiple conditions.

    • In this case, we are categorizing pizzas as either regular pizzas (e.g., pepperoni, sausage) or specialty pizzas (e.g., breakfast, margherita, BBQ).

    • To achieve this, we use Python’s if-elif-else syntax, which allows us to evaluate multiple conditions efficiently.

    • Example:

python
1requested_pizzas = ["pepperoni", "sausage", "breakfast", "margherita", "bbq"]
2
3if requested_pizzas:
4    for requested_pizza in requested_pizzas:
5        if requested_pizza == "pepperoni" or requested_pizza == "sausage":
6            print("Preparing " + requested_pizza + " pizza (a regular pizza)")
7        elif requested_pizza == "breakfast" or requested_pizza == "margherita" \
8        or requested_pizza == "bbq":
9            print("Preparing " + requested_pizza + " pizza (a specialty pizza)")
10        else:
11            print("Sorry, we don't have " + requested_pizza + " pizza available.")
12else:
13    print("No pizzas to be prepared.")
  • Output:
1Preparing pepperoni pizza (a regular pizza)
2Preparing sausage pizza (a regular pizza)
3Preparing breakfast pizza (a specialty pizza)
4Preparing margherita pizza (a specialty pizza)
5Preparing bbq pizza (a specialty pizza)