if, elif, else, and conditionals | Python

Programs need to make decisions: run one block of code if a condition is true, another if it is false. Python handles this with if, elif, and else.

The basic if statement

An if statement runs a block of code only when its condition is true:

temperature = 30

if temperature > 25:
    print("It's warm outside.")

The condition follows the if keyword. A colon : marks the start of the block. The block is indented — Python uses indentation, not braces, to define code blocks.

if / else

Add else to provide an alternative when the condition is false:

temperature = 15

if temperature > 25:
    print("It's warm outside.")
else:
    print("It's cold outside.")

Only one branch runs. If the if condition is true, the else block is skipped entirely.

if / elif / else

Use elif (short for “else if”) to check multiple conditions in sequence:

temperature = 20

if temperature > 30:
    print("It's hot.")
elif temperature > 20:
    print("It's warm.")
elif temperature > 10:
    print("It's cool.")
else:
    print("It's cold.")

Python evaluates conditions top to bottom. The first true condition wins and the rest are skipped. If none are true, the else block runs.

The order matters. A more general condition should come after more specific ones:

# Wrong — the first condition catches everything
if temperature > 10:
    print("above 10")
elif temperature > 20:    # never reached
    print("above 20")

Nested conditionals

You can place if statements inside other if statements:

age = 25
has_id = True

if age >= 18:
    if has_id:
        print("Entry allowed.")
    else:
        print("ID required.")
else:
    print("Must be 18 or older.")

Nesting works but gets hard to read quickly. Often you can combine conditions with and / or instead:

if age >= 18 and has_id:
    print("Entry allowed.")
elif age >= 18:
    print("ID required.")
else:
    print("Must be 18 or older.")

Logical operators

Combine conditions with and, or, and not:

age = 25
has_ticket = True

if age >= 18 and has_ticket:
    print("Entry allowed.")

if age < 12 or age >= 65:
    print("Discount available.")

if not has_ticket:
    print("Ticket required.")

and — true when both sides are true
or — true when at least one side is true
not — inverts the boolean value

Truthy and falsy values

Python does not require conditions to be actual booleans. Any value can be used in an if statement. Python evaluates it as true or false using these rules:

The following values are falsy (treated as false):

False
None
0 (integer zero)
0.0 (float zero)
"" (empty string)
[] (empty list)
{} (empty dictionary)

Everything else is truthy (treated as true):

non-zero numbers
non-empty strings
non-empty collections
most objects

This lets you write concise checks:

name = ""

if name:
    print(f"Hello, {name}")
else:
    print("Name is empty.")

The ternary expression

Python has a compact form of if/else for simple value selection:

status = "active" if is_logged_in else "guest"

This is an expression — it produces a value. It reads as: value_if_true if condition else value_if_false.

Use this for simple assignments. For anything more complex, use a full if/else block.

Common patterns

Checking membership

Use in to test if a value exists in a collection:

role = "admin"

if role in ("admin", "moderator"):
    print("Access granted.")

Checking for None

Use is or is not to check for None:

result = None

if result is None:
    print("No result found.")

if result is not None:
    print(f"Result: {result}")

is checks identity — whether two names refer to the exact same object in memory. Since there is only one None value in Python, identity checking is the correct way to test for it. Using == None works in most cases but can behave unexpectedly with custom objects that override equality.

What to carry forward

if runs a block when its condition is true
elif checks additional conditions in order; only the first match runs
else catches everything that did not match earlier conditions
Python uses indentation, not braces, for code blocks
and, or, not combine and invert conditions
many values besides False are falsy — 0, "", [], {}, None
use is / is not to check for None
value if condition else alternative is a compact ternary expression

Conditionals let your code respond to different situations. The next lesson covers loops, which let your code repeat actions.