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if Statements

Decision-making is a fundamental concept in programming, and the if-elif-else statement in Python is a powerful tool for precisely that purpose. These statements allow you to create dynamic, branching logic within your programs. With them, you can instruct your code to take different actions based on specific conditions, making your programs more intelligent and responsive.

What & Why?

An if-elif-else statement is a control structure in Python that enables your program to make choices. It starts with an if statement that checks a particular condition. If that condition is True, a specific block of code is executed. However, if the condition is not met, the program can continue to evaluate other conditions using elif (short for “else if”) statements. These elif clauses allow for multiple conditions to be checked sequentially. Finally, if none of the preceding conditions are True, the else code block is executed.

See Also

if/else statements evaluate to True or False - which are boolean values. See Booleans for more details.

The primary purpose of if-elif-else statements is to introduce decision-making capabilities into your code. They allow your program to adapt and respond to varying situations. There are three examples below of how you might use if-elif-else statements to implement logic:

Example 1: Game Over Conditions

If-Else Statement Use Case: Game Over Conditions
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# Determine if a player’s score has reached a winning threshold.
# If yes, declare a winner; otherwise, continue the game.

player_1_score = 47

if (player_1_score >= 100):
    print("YOU WIN!")
else:
    print(f"You need {100 - player_1_score} more points to win!")
Would return: 
You need 53 more points to win!

Example 2: User Authentication

If-Else Statement Use Case: User Authentication
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# Check if a user’s credentials are correct.
# If they are, grant access; otherwise, deny access.

user_input_username = "john_doe"
user_input_password = "secure_password"

correct_username = "john_doe"
correct_password = "secure_password"

if user_input_username == correct_username and \ # (1)
    user_input_password == correct_password:
     print("Access granted!")
else:
     print("Access denied. Please check your username and password.")
  1. The preceeding backslash is a line continuation. Both of these conditions are evaluated in the if statement.

Would result in: 

Access granted!

Example 3: Grade Evaluation

If-Else Statement Use Case: Grade Evaluation
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# Determine a student's letter grade based on their numeric grade.

student_score = 85

if student_score >= 90:
    print("A")
elif student_score >= 80:
    print("B")
elif student_score >= 70:
    print("C")
elif student_score >= 60:
    print("D")
else:
    print("F")

Would output:

B

In these examples, if-elif-else statements allow the program to take different actions depending on specific conditions. They provide the flexibility to handle a wide range of scenarios and are essential for building responsive and intelligent software.