+++ slug = "conditionals" title = "Conditionals" section = "Control Flow" summary = "if, elif, and else choose which block runs." doc_path = "/tutorial/controlflow.html#if-statements" see_also = [ "booleans", "truthiness", "guard-clauses", "match-statements", ] +++

if, elif, and else let a program choose one path based on a condition. Python uses indentation to show which statements belong to each branch.

Conditions use Python truthiness: booleans work directly, and many objects such as empty lists or empty strings are considered false. Order branches from most specific to most general.

Use elif to keep one decision flat instead of nested. Use Python's ternary expression only when you are choosing between two values.

:::program

temperature = 72

if temperature < 60:
    print("cold")
elif temperature < 80:
    print("comfortable")
else:
    print("hot")

items = ["coat", "hat"]
if items:
    print(f"packing {len(items)} items")

status = "ok" if temperature < 90 else "danger"
print(status)

:::

:::cell Start with the value that the branches will test. A conditional is only useful when the branch condition is visible and meaningful.

Use if, elif, and else for one ordered choice. Python tests the branches from top to bottom and runs only the first matching block.

temperature = 72

if temperature < 60:
    print("cold")
elif temperature < 80:
    print("comfortable")
else:
    print("hot")

comfortable

:::

:::cell Truthiness is part of conditional flow. Empty collections are false, so if items: reads as “if there is anything to work with.”

items = ["coat", "hat"]
if items:
    print(f"packing {len(items)} items")

packing 2 items

:::

:::cell Use the ternary expression when you are choosing a value. If either side needs multiple statements, use a normal if block instead.

status = "ok" if temperature < 90 else "danger"
print(status)

ok

:::

:::note

• Python has no mandatory parentheses around conditions; the colon and indentation define the block.
• Comparison operators such as < and == can be chained, as in 0 < value < 10.
• Keep branch bodies short; move larger work into functions so the decision remains easy to scan. :::