Python · Const

if

Python’s if statement conditionally executes one suite. It checks the if and optional elif conditions in order, running the first matching suite or an optional else fallback.

How it works

An if statement evaluates its conditions from top to bottom. It executes only the suite belonging to the first true condition; if none is true, an optional else suite runs. Each suite is a colon-terminated, indented block.

Syntax

if test1:
    suite
elif test2:
    suite
else:
    suite

Parameters

Name	Type	Description
`test / assignment_expression`	`expression`	An expression whose truth value determines whether its suite is selected.
`suite`	`suite`	The statement block executed when its associated condition is selected.

Key points

Use if to run a block only when its condition is true.
Python checks conditions sequentially and selects exactly one suite.
A condition uses Python’s normal truth-value rules, as defined for Boolean operations.
Each elif adds another condition-and-block alternative.

Common mistakes

Only one branch executes: after the first true condition, later conditions and suites are not evaluated.
An else suite runs only when every if and elif condition is false.

Example: Conditional status selection

temperature = 22

if temperature < 0:
    status = "freezing"
elif temperature == 0:
    status = "freezing point"
else:
    status = "above freezing"

print(status)

Evaluates the conditions in order and prints the status for the first true condition.

When to use it

Guard invalid or missing values

Validate request input or configuration before processing it.

Select a control-flow path

Choose behavior based on a state, role, or feature flag.

Handle fallback behavior

Provide a default action when no expected condition matches.

Interview questions

QHow does Python choose which branch of an if statement to execute?

The conditions are evaluated in order, and the suite associated with the first true condition runs. No other part of that if statement is executed or evaluated.

Follow-up: What happens when all conditions are false? If an else clause exists, its suite executes; otherwise, the statement performs no branch action.

QWhat are the roles of elif and else?

elif clauses provide additional conditions after the initial if, and an else clause is optional. The grammar permits zero or more elif clauses followed by at most one else clause.

Follow-up: Can an if statement have multiple else clauses? No; its grammar permits only an optional single else clause at the end.

QWhat is the basic syntax of an if statement?

The condition is an assignment_expression, followed by a colon and a suite. A suite is the block of statements controlled by that clause, normally written as an indented block.

Follow-up: Can suites be written on one line? Yes, Python permits a simple suite after the colon, though multiline indentation is generally clearer for substantial logic.

elif
else
while
for
Boolean operations
conditional expression

Source: 8. Compound statements — Python 3.15.0 documentation. Checked 2026-10-16.

if