Expressions

Expressions get replaced with values when a template is rendered.

Expressions appear inside {{ ... }} tags.

Literals

The simplest form of expressions.

Boolean

true is always true and false is always false.

true
false

Dict

A dict in Python is a structure that combines keys and values.

Keys must be unique and always have exactly one value.

{
  "foo": "Hello World"
}

Integers

Integers are whole numbers without a decimal part.

The underscore (_) character can be used to separate groups for legibility.

42
123_456

Floating point numbers

Floating Point Numbers can be written using a period (.) as a decimal mark.

They can be written in scientific notation with an upper or lowercase e to indicate the exponent part.

The underscore (_) character can be used to separate groups for legibility, but cannot be used in the exponent part.

42.23
42.1e2
123_456.789

List

Everything between two square brackets is a list ([...]).

Lists are useful for storing sequential data to be iterated over.

["List", "of", "Objects"]

String

Everything between two double or single quotes is a string.

They are useful whenever you need a string in the template.

"Hello World"

Tuples

Tuples are similar to lists that cannot be modified (“immutable”) and usually used to represent items of two or more elements.

If a tuple only has one item, it must be followed by a comma.

("Tuple",)
("Tuple", "of", "values")

Math

Add

Adds two objects together.

Usually the objects are numbers. See the ~ operator for string concatenation.

{{ 1 + 1 }}

=> 2

Subtract

Subtracts the second number from the first number.

{{ 3 - 2 }}

=> 1

Divide

Divide two numbers

The return value will be a Floating Point Number.

{{ 1 / 2 }}

=> 0.5

Divide two numbers and return the truncated integer result

{{ 20 // 7 }}

=> 2

Calculate the remainder of an integer division

{{ 11 % 7 }}

=> 4

Multiply

Multiply the left operand with the right one.

This can also be used to repeat a string multiple times.

{{ 2 * 2 }}

=> 4

{{ "!" * 8 }}

=> !!!!!!!!

Raise to the power

Raise the left operand to the power of the right operand.

{{ 2 ** 3 }}

=> 8

Comparisons

Equality (==)

Compares two objects for equality.

{{ "hello" == "hello" }}

=> true

Inequality (!=)

Compares two objects for inequality.

{{ "hello" != "hello" }}

=> false

Greater than (>)

Left hand side is greater than the right hand side.

{{ 5 > 4 }}

=> true

Greater than or equal to (>=)

Left hand side is greater or equal to the right hand side.

{{ 5 >= 5 }}

=> true

Less than (<)

Left hand side is lower than the right hand side.

{{ 5 < 4 }}

=> false

Less than or equal to (<=)

Left hand side is lower or equal to the right hand side.

{{ 5 <= 5 }}

=> true

Logic

and

Returns true if the left and the right operand are true.

{% set foo = 2 %}
{{ foo > 1 and foo < 5 }}

=> true

or

Returns true if the left or the right operand are true.

{% set foo = 3 %}
{{ foo < 5 or foo == 3 }}

=> true

not

Negates a statement using the is and in operators. All other expressions will require a prefix notation.

{{ foo is not bar }}
{{ foo not in bar }}
{{ not (foo and bar) }}

(expr)

Group expressions in parentheses.

{% set foo = 2 %}
{{ (foo > 1) and (foo < 5) }}

=> true

Other operators

in

Perform a sequence or mapping containment test. Returns true if the left operand is contained in the right.

{{ 1 in [1, 2, 3] }}

=> true

is

Performs a Test.

{{ foo is bar }}

|

Applies a Filter.

{{ foo | lower }}

~

Converts all operands into strings and concatenates them.

{% set foo = "world" %}
{{ "Hello " ~ foo ~ "!" }}

=> Hello world!

. or []

Get an attribute of an object.

{{ foo.bar }}
{{ foo["bar"] }}

If expression

Learn about using inline if expressions.

This is useful in some situations. The general syntax is:

{# <do something> if <something is true> else <do something else> #}
{{ "[{}]".format(page.title) if page.title }}

The else part is optional. If not provided, the else block implicitly evaluates into an Undefined object.

Also refer to Control Structures: if.