Python Core | VoidX Academy

6. Python If / Else

Control Flow

Python If / Else

A program that runs the same code every time regardless of conditions is not very useful. Conditional statements let your program make decisions — executing certain blocks of code only when specific conditions are met.

In Python, the keywords if, elif, and else are the building blocks of all decision-making logic. Every login check, every form validation, every game rule comes down to these three keywords.

The if Statement

The if statement evaluates a condition. If that condition is True, the indented block of code beneath it runs. If it is False, Python skips that block entirely.

temperature = 35

if temperature > 30:
    print("It is a hot day.")
    print("Stay hydrated!")

OutputIt is a hot day. Stay hydrated!

The colon : after the condition is mandatory. The indented lines below form the body of the if block. Python uses indentation (4 spaces is the standard) to define which lines belong to the block.

The else Clause

The else clause defines what happens when the if condition is False. It is optional but covers the case where none of the conditions matched.

temperature = 18

if temperature > 30:
    print("It is a hot day.")
else:
    print("It is a cool day.")
    print("Maybe bring a jacket.")

OutputIt is a cool day. Maybe bring a jacket.

Exactly one branch of an if/else will always execute. Never both, never neither (as long as there is an else).

The elif Clause

elif is short for "else if." It lets you chain multiple conditions together. Python evaluates them top to bottom and executes the first one that is True, then skips all the rest.

score = 72

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

OutputGrade: C

Even though score >= 70 and score >= 60 are both True for score = 72, Python stops at the first True condition and never checks the rest.

Nested if

You can place an if statement inside another if statement. This is called nesting. It lets you check secondary conditions only when a primary condition has already passed.

age = 20
has_id = True

if age >= 18:
    print("Age check passed.")
    if has_id:
        print("ID check passed. Access granted.")
    else:
        print("No ID presented. Access denied.")
else:
    print("Under 18. Access denied.")

OutputAge check passed. ID check passed. Access granted.

💡Clean Code Tip: Deeply nested if statements (more than 2–3 levels) become very hard to read and maintain. A common refactoring technique is early return — checking for the failure case first and returning early, keeping the happy path un-nested.

Short-hand if (One-liner)

If the body of an if statement is a single line, you can write it on the same line as the condition. This is called the short-hand if or one-liner syntax.

x = 15

if x > 10: print("x is greater than 10")

# Works for else too on one line:
if x > 10: print("Big")
else: print("Small")

Outputx is greater than 10 Big

Ternary Operator (Short-hand if-else)

Python has a concise one-line ternary expression that assigns one of two values based on a condition. The syntax is: value_if_true if condition else value_if_false.

age = 20
status = "adult" if age >= 18 else "minor"
print(status)

# Works directly inside print too
points = 85
print("Pass" if points >= 50 else "Fail")

Outputadult Pass

The ternary operator is ideal for simple assignments where the logic is clear at a glance. For complex logic with multiple conditions, always use the full if/elif/else format for readability.

The pass Statement

Python does not allow empty code blocks — a block with no statements is a SyntaxError. The pass keyword is a placeholder that does absolutely nothing. It tells Python "this block is intentionally empty for now."

user_role = "guest"

if user_role == "admin":
    pass   # TODO: implement admin dashboard
else:
    print("Welcome, guest!")

OutputWelcome, guest!

pass is used during development as a stub — you define the structure of your code first, put pass inside empty blocks, and fill in the logic later. It is also used in empty class and function definitions.

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