Jinja filters

From Leo's Notes
Last edited on 15 February 2022, at 00:39.

Jinja filters allow you to run functions on some data right before it is rendered. It does not change the underlying data in anyway.

Quick introduction

  • Filters are applied using the pipe | operator.
  • You can chain multiple filters one after another to create a pipeline.
  • Some filters requires arguments. Pass them in as if calling a function.


All filters that create Lists or work on Lists create Generator objects instead of Lists. To convert these objects back to Lists, use "list" filter at the end


String filters

Function Example
upper, lower Converts string to upper or lower case apple | upper
replace(old, new, count=None) Replaces all or a specified number of occurrences of the old substring with the new substring apple | replace('a', 'b')
center(width=80) Centers the text based on the given width.

Note: there is no 'left' or 'right' filter. If you need to left or right align text, use format instead.

escape or e converted into html safe sequence by sanitising '&', '<', '>', ‘ (singlequote), and ” (doublequote).
indent(width=4, first=False, blank=False) Indents text
capitalize The first character of the string is uppercased apple | capitalize
title Uppercases every word
trim Removes excess leading/trailing spaces
truncate(length=255, killwords=False, end='...', ) Truncates a string to the given length. Optionally specifies suffix if truncation happened.
wordwrap(width=79, break_long_words=True, wrapstring=None) Line wraps the given text into a specified column width.


Iterables include lists, tuples, strings, and dictionaries.

Function Example
first / last / random Selects the first / last / or random item
batch Batches list items together items = [1, 2, 3, 4, 5]

items | batch(2, fill_with=8) | list

Output: [ [1, 2], [3, 4], [5, 8 ] ]

slice Slices a list into the given number of slices items = [1, 2, 3, 4, 5]

items | slice(2, fill_with=8) | list

Output: [ [1, 2, 3], [4, 5, 8 ] ]

map(attribute=attributeName) myDictList = [ {'a': 1, 'b': 2}, {'a': 3, 'b': 4}, {'a': 5, 'b': 6} ]

myDictList | map(attribute='a') | list

Output: [1, 3, 5]

map(filter) Apply the given filter to every item in the list
reject(test) / select(test) Removes or retains items that fail the test
rejectattr(attribute, test, args)

selectattr(attribute, test, args)

Removes or retains items that have an attribute myDict = ({'a': 0}, {'a': 1}, {'a': 2}) %}

myDict | rejectattr('a', 'equalto', 1) | list

Output: [{'a': 0}, {'a': 2}]

unique returns all unique values
sort(reverse=False, case_sensitive=False, attribute=None) sort
reverse reverses order
shuffle randomly orders the list

Data types

Function Example
float(default) / int(default, base=10)
string Converts to Unicode string
list converts any iterable to a list
default(default='', bool=false) Provides a default value if the value is undefined. If given bool is true, None or empty string will be treated as undefined.
filesizeformat Converts to human readable sizes
from_json / json Converts from json to a dictionary object or an object into json.
length / count length of string or number of objects in a list

See also