Conditional statements with if

The if statement is used to implement decisions and branching in a program. One or more instructions are only executed if a condition matches:

if name == 'Emily':
    studies = 'Physics'

There must be an if block, zero or more elif’s and an optional else block:

if name == 'Emily':
    studies = 'Physics'
elif name == 'Maria':
    studies = 'Computer Science'
elif name == 'Sarah':
    studies = 'Archaeology'
else:
    studies = '-- not registered yet --'

Code blocks

After an if statement, all indented commands are treated as a code block, and are executed in the context of the condition.

The next unindented command is executed in any case.

Comparison operators

An if expression may contain comparison operators like:

a == b
a != b
a < b
a > b
a <= b
a >= b

On lists and strings you can also use:

a in b

Multiple expressions can be combined with boolean logic (and, or, not):

a or b
a and b
not a
(a or b) and not (c or d)

Boolean value of variables

Each variable can be interpreted as a boolean (True/False) value. All values are treated as True, except for:

False
0
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