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3c8b7ad @mitsuhiko first version of the jinja2 docs
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1 Template Designer Documentation
2 ===============================
3
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4 .. highlight:: html+jinja
5
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6 This document describes the syntax and semantics of the template engine and
7 will be most useful as reference to those creating Jinja templates. As the
8 template engine is very flexible the configuration from the application might
9 be slightly different from here in terms of delimiters and behavior of
10 undefined values.
11
12
13 Synopsis
14 --------
15
16 A template is simply a text file. It can generate any text-based format
17 (HTML, XML, CSV, LaTeX, etc.). It doesn't have a specific extension,
18 ``.html`` or ``.xml`` are just fine.
19
20 A template contains **variables** or **expressions**, which get replaced with
21 values when the template is evaluated, and tags, which control the logic of
22 the template. The template syntax is heavily inspired by Django and Python.
23
24 Below is a minimal template that illustrates a few basics. We will cover
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25 the details later in that document::
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26
27 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
28 <html lang="en">
29 <head>
30 <title>My Webpage</title>
31 </head>
32 <body>
33 <ul id="navigation">
34 {% for item in navigation %}
35 <li><a href="{{ item.href }}">{{ item.caption }}</a></li>
36 {% endfor %}
37 </ul>
38
39 <h1>My Webpage</h1>
40 {{ a_variable }}
41 </body>
42 </html>
43
44 This covers the default settings. The application developer might have
45 changed the syntax from ``{% foo %}`` to ``<% foo %>`` or something similar.
46
47 There are two kinds of delimiers. ``{% ... %}`` and ``{{ ... }}``. The first
48 one is used to execute statements such as for-loops or assign values, the
49 latter prints the result of the expression to the template.
50
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51 .. _variables:
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52
53 Variables
54 ---------
55
56 The application passes variables to the templates you can mess around in the
57 template. Variables may have attributes or elements on them you can access
58 too. How a variable looks like, heavily depends on the application providing
59 those.
60
61 You can use a dot (``.``) to access attributes of a variable, alternative the
62 so-called "subscribe" syntax (``[]``) can be used. The following lines do
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63 the same::
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64
65 {{ foo.bar }}
66 {{ foo['bar'] }}
67
68 It's important to know that the curly braces are *not* part of the variable
69 but the print statement. If you access variables inside tags don't put the
70 braces around.
71
72 If a variable or attribute does not exist you will get back an undefined
73 value. What you can do with that kind of value depends on the application
74 configuration, the default behavior is that it evaluates to an empty string
75 if printed and that you can iterate over it, but every other operation fails.
76
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77 .. _filters:
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78
79 Filters
80 -------
81
82 Variables can by modified by **filters**. Filters are separated from the
83 variable by a pipe symbol (``|``) and may have optional arguments in
84 parentheses. Multiple filters can be chained. The output of one filter is
85 applied to the next.
86
87 ``{{ name|striptags|title }}`` for example will remove all HTML Tags from the
88 `name` and title-cases it. Filters that accept arguments have parentheses
89 around the arguments, like a function call. This example will join a list
90 by spaces: ``{{ list|join(', ') }}``.
91
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92 The :ref:`builtin-filters` below describes all the builtin filters.
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93
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94 .. _tests:
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95
96 Tests
97 -----
98
99 Beside filters there are also so called "tests" available. Tests can be used
100 to test a variable against a common expression. To test a variable or
101 expression you add `is` plus the name of the test after the variable. For
102 example to find out if a variable is defined you can do ``name is defined``
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103 which will then return true or false depending on if `name` is defined.
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104
105 Tests can accept arguments too. If the test only takes one argument you can
106 leave out the parentheses to group them. For example the following two
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107 expressions do the same::
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108
109 {% if loop.index is divisibleby 3 %}
110 {% if loop.index is divisibleby(3) %}
111
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112 The :ref:`builtin-tests` below describes all the builtin tests.
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113
114
115 Comments
116 --------
117
118 To comment-out part of a line in a template, use the comment syntax which is
119 by default set to ``{# ... #}``. This is useful to comment out parts of the
120 template for debugging or to add information for other template designers or
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121 yourself::
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122
123 {# note: disabled template because we no longer user this
124 {% for user in users %}
125 ...
126 {% endfor %}
127 #}
128
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129
130 Whitespace Control
131 ------------------
132
133 In the default configuration whitespace is not further modified by the
134 template engine, so each whitespace (spaces, tabs, newlines etc.) is returned
135 unchanged. If the application configures Jinja to `trim_blocks` the first
136 newline after a a template tag is removed automatically (like in PHP).
137
138 But you can also strip whitespace in templates by hand. If you put an minus
139 sign (``-``) to the start or end of an block (for example a for tag), a
140 comment or variable expression you can remove the whitespaces after or before
141 that block::
142
143 {% for item in seq -%}
144 {{ item }}
145 {%- endfor %}
146
147 This will yield all elements without whitespace between them. If `seq` was
148 a list of numbers from ``1`` to ``9`` the output would be ``123456789``.
149
150 Note that you must not use a whitespace between the tag and the minus sign:
151
152 valid:
153 {%- if foo -%}...{% endif %}
154
155 invalid:
156
157 {% - if foo - %}...{% endif %}
158
159 If :ref:`line-statements` are enabled they strip leading whitespace
160 automatically up to the beginning of the line.
161
162
163 Escaping
164 --------
165
166 It is sometimes desirable or even necessary to have Jinja ignore parts it
167 would otherwise handle as variables or blocks. For example if the default
168 syntax is used and you want to use ``{{`` as raw string in the template and
169 not start a variable you have to use a trick.
170
171 The easiest way is to output the variable delimiter (``{{``) by using a
172 variable expression::
173
174 {{ '{{' }}
175
176 For bigger sections it makes sense to mark a block `raw`. For example to
177 put Jinja syntax as example into a template you can use this snippet::
178
179 {% raw %}
180 <ul>
181 {% for item in seq %}
182 <li>{{ item }}</li>
183 {% endfor %}
184 </ul>
185 {% endraw %}
186
187
188 .. _line-statements:
189
190 Line Statements
191 ---------------
192
193 If line statements are enabled by the application it's possible to mark a
194 line as a statement. For example if the line statement prefix is configured
195 to ``#`` the following two examples are equivalent::
196
197 <ul>
198 # for item in seq
199 <li>{{ item }}</li>
200 # endfor
201 </ul>
202
203 <ul>
204 {% for item in seq %}
205 <li>{{ item }}</li>
206 {% endfor %}
207 </ul>
208
209 The line statement prefix can appear anywhere on the line as long as no text
210 precedes it. For better readability statements that start a block (such as
211 `for`, `if`, `elif` etc.) may end with a colon::
212
213 # for item in seq:
214 ...
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215 # endfor
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216
217
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218 .. _template-inheritance:
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219
220 Template Inheritance
221 --------------------
222
223 The most powerful part of Jinja is template inheritance. Template inheritance
224 allows you to build a base "skeleton" template that contains all the common
225 elements of your site and defines **blocks** that child templates can override.
226
227 Sounds complicated but is very basic. It's easiest to understand it by starting
228 with an example.
229
230
231 Base Template
232 ~~~~~~~~~~~~~
233
234 This template, which we'll call ``base.html``, defines a simple HTML skeleton
235 document that you might use for a simple two-column page. It's the job of
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236 "child" templates to fill the empty blocks with content::
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237
238 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
239 <html lang="en">
240 <html xmlns="http://www.w3.org/1999/xhtml">
241 <head>
242 {% block head %}
243 <link rel="stylesheet" href="style.css" />
244 <title>{% block title %}{% endblock %} - My Webpage</title>
245 {% endblock %}
246 </head>
247 <body>
248 <div id="content">{% block content %}{% endblock %}</div>
249 <div id="footer">
250 {% block footer %}
251 &copy; Copyright 2008 by <a href="http://domain.invalid/">you</a>.
252 {% endblock %}
253 </div>
254 </body>
255
256 In this example, the ``{% block %}`` tags define four blocks that child templates
257 can fill in. All the `block` tag does is to tell the template engine that a
258 child template may override those portions of the template.
259
260 Child Template
261 ~~~~~~~~~~~~~~
262
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263 A child template might look like this::
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264
265 {% extends "base.html" %}
266 {% block title %}Index{% endblock %}
267 {% block head %}
268 {{ super() }}
269 <style type="text/css">
270 .important { color: #336699; }
271 </style>
272 {% endblock %}
273 {% block content %}
274 <h1>Index</h1>
275 <p class="important">
276 Welcome on my awsome homepage.
277 </p>
278 {% endblock %}
279
280 The ``{% extends %}`` tag is the key here. It tells the template engine that
281 this template "extends" another template. When the template system evaluates
282 this template, first it locates the parent. The extends tag should be the
283 first tag in the template. Everything before it is printed out normally and
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284 may cause confusion. For details about this behavior and how to take
285 advantage of it, see :ref:`null-master-fallback`.
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286
287 The filename of the template depends on the template loader. For example the
288 :class:`FileSystemLoader` allows you to access other templates by giving the
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289 filename. You can access templates in subdirectories with an slash::
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290
291 {% extends "layout/default.html" %}
292
293 But this behavior can depend on the application embedding Jinja. Note that
294 since the child template doesn't define the ``footer`` block, the value from
295 the parent template is used instead.
296
297 You can't define multiple ``{% block %}`` tags with the same name in the
298 same template. This limitation exists because a block tag works in "both"
299 directions. That is, a block tag doesn't just provide a hole to fill - it
300 also defines the content that fills the hole in the *parent*. If there
301 were two similarly-named ``{% block %}`` tags in a template, that template's
302 parent wouldn't know which one of the blocks' content to use.
303
304 If you want to print a block multiple times you can however use the special
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305 `self` variable and call the block with that name::
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306
307 <title>{% block title %}{% endblock %}</title>
308 <h1>{{ self.title() }}</h1>
309 {% block body %}{% endblock %}
310
311
312 Unlike Python Jinja does not support multiple inheritance. So you can only have
313 one extends tag called per rendering.
314
315
316 Super Blocks
317 ~~~~~~~~~~~~
318
319 It's possible to render the contents of the parent block by calling `super`.
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320 This gives back the results of the parent block::
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321
322 {% block sidebar %}
323 <h3>Table Of Contents</h3>
324 ...
325 {{ super() }}
326 {% endblock %}
327
328
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329 Named Block End-Tags
330 ~~~~~~~~~~~~~~~~~~~~
331
332 Jinja2 allows you to put the name of the block after the end tag for better
333 readability::
334
335 {% block sidebar %}
336 {% block inner_sidebar %}
337 ...
338 {% endblock inner_sidebar %}
339 {% endblock sidebar %}
340
341 However the name after the `endblock` word must match the block name.
342
343
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344 HTML Escaping
345 -------------
346
347 When generating HTML from templates, there's always a risk that a variable will
348 include characters that affect the resulting HTML. There are two approaches:
349 manually escaping each variable or automatically escaping everything by default.
350
351 Jinja supports both, but what is used depends on the application configuration.
352 The default configuaration is no automatic escaping for various reasons:
353
354 - escaping everything except of safe values will also mean that Jinja is
355 escaping variables known to not include HTML such as numbers which is
356 a huge performance hit.
357
358 - The information about the safety of a variable is very fragile. It could
359 happen that by coercing safe and unsafe values the return value is double
360 escaped HTML.
361
362 Working with Manual Escaping
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363 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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364
365 If manual escaping is enabled it's **your** responsibility to escape
366 variables if needed. What to escape? If you have a variable that *may*
367 include any of the following chars (``>``, ``<``, ``&``, or ``"``) you
368 **have to** escape it unless the variable contains well-formed and trusted
369 HTML. Escaping works by piping the variable through the ``|e`` filter:
370 ``{{ user.username|e }}``.
371
372 Working with Automatic Escaping
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373 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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374
375 When automatic escaping is enabled everything is escaped by default except
376 for values explicitly marked as safe. Those can either be marked by the
377 application or in the template by using the `|safe` filter. The main
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378 problem with this approach is that Python itself doesn't have the concept
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379 of tainted values so the information if a value is safe or unsafe can get
380 lost. If the information is lost escaping will take place which means that
381 you could end up with double escaped contents.
382
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383 Double escaping is easy to avoid however, just rely on the tools Jinja2
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384 provides and don't use builtin Python constructs such as the string modulo
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385 operator.
386
387 Functions returning template data (macros, `super`, `self.BLOCKNAME`) return
388 safe markup always.
389
390 String literals in templates with automatic escaping are considered unsafe
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391 too. The reason for this is that the safe string is an extension to Python
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392 and not every library will work properly with it.
393
394
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395 List of Control Structures
396 --------------------------
397
398 A control structure refers to all those things that control the flow of a
399 program - conditionals (i.e. if/elif/else), for-loops, as well as things like
400 macros and blocks. Control structures appear inside ``{% ... %}`` blocks
401 in the default syntax.
402
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403 For
404 ~~~
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405
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406 Loop over each item in a sequence. For example, to display a list of users
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407 provided in a variable called `users`::
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408
409 <h1>Members</h1>
410 <ul>
411 {% for user in users %}
412 <li>{{ user.username|e }}</li>
413 {% endfor %}
414 </ul>
415
416 Inside of a for loop block you can access some special variables:
417
418 +-----------------------+---------------------------------------------------+
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419 | Variable | Description |
420 +=======================+===================================================+
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421 | `loop.index` | The current iteration of the loop. (1 indexed) |
422 +-----------------------+---------------------------------------------------+
423 | `loop.index0` | The current iteration of the loop. (0 indexed) |
424 +-----------------------+---------------------------------------------------+
425 | `loop.revindex` | The number of iterations from the end of the loop |
426 | | (1 indexed) |
427 +-----------------------+---------------------------------------------------+
428 | `loop.revindex0` | The number of iterations from the end of the loop |
429 | | (0 indexed) |
430 +-----------------------+---------------------------------------------------+
431 | `loop.first` | True if first iteration. |
432 +-----------------------+---------------------------------------------------+
433 | `loop.last` | True if last iteration. |
434 +-----------------------+---------------------------------------------------+
435 | `loop.length` | The number of items in the sequence. |
436 +-----------------------+---------------------------------------------------+
437 | `loop.cycle` | A helper function to cycle between a list of |
438 | | sequences. See the explanation below. |
439 +-----------------------+---------------------------------------------------+
440
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441 Within a for-loop, it's possible to cycle among a list of strings/variables
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442 each time through the loop by using the special `loop.cycle` helper::
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443
444 {% for row in rows %}
445 <li class="{{ loop.cycle('odd', 'even') }}">{{ row }}</li>
446 {% endfor %}
447
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448 .. _loop-filtering:
449
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450 Unlike in Python it's not possible to `break` or `continue` in a loop. You
451 can however filter the sequence during iteration which allows you to skip
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452 items. The following example skips all the users which are hidden::
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453
454 {% for user in users if not user.hidden %}
455 <li>{{ user.username|e }}</li>
456 {% endfor %}
457
458 The advantage is that the special `loop` variable will count correctly thus
459 not counting the users not iterated over.
460
461 If no iteration took place because the sequence was empty or the filtering
462 removed all the items from the sequence you can render a replacement block
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463 by using `else`::
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464
465 <ul>
466 {% for user in users %}
467 <li>{{ user.username|e }}</li>
468 {% else %}
469 <li><em>no users found</em></li>
470 {% endif %}
471 </ul>
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472
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473 It is also possible to use loops recursively. This is useful if you are
474 dealing with recursive data such as sitemaps. To use loops recursively you
475 basically have to add the `recursive` modifier to the loop definition and
476 call the `loop` variable with the new iterable where you want to recurse.
477
478 The following example implements a sitemap with recursive loops::
479
480 <ul class="sitemap">
481 {%- for item in sitemap recursive %}
482 <li><a href="{{ item.href|e }}">{{ item.title }}</a>
483 {%- if item.children -%}
484 <ul class="submenu">{{ loop(item.children) }}</ul>
485 {%- endif %}</li>
486 {%- endfor %}
487 </ul>
488
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489
490 If
491 ~~
492
493 The `if` statement in Jinja is comparable with the if statements of Python.
494 In the simplest form you can use it to test if a variable is defined, not
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495 empty or not false::
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496
497 {% if users %}
498 <ul>
499 {% for user in users %}
500 <li>{{ user.username|e }}</li>
501 {% endfor %}
502 </ul>
503 {% endif %}
504
505 For multiple branches `elif` and `else` can be used like in Python. You can
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506 use more complex :ref:`expressions` there too::
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507
508 {% if kenny.sick %}
509 Kenny is sick.
510 {% elif kenny.dead %}
511 You killed Kenny! You bastard!!!
512 {% else %}
513 Kenny looks okay --- so far
514 {% endif %}
515
516 If can also be used as :ref:`inline expression <if-expression>` and for
517 :ref:`loop filtering <loop-filtering>`.
518
519
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520 Macros
521 ~~~~~~
522
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523 Macros are comparable with functions in regular programming languages. They
524 are useful to put often used idioms into reusable functions to not repeat
525 yourself.
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526
527 Here a small example of a macro that renders a form element::
528
529 {% macro input(name, value='', type='text', size=20) -%}
530 <input type="{{ type }}" name="{{ name }}" value="{{
531 value|e }}" size="{{ size }}">
532 {%- endmacro %}
533
534 The macro can then be called like a function in the namespace::
535
536 <p>{{ input('username') }}</p>
537 <p>{{ input('password', type='password') }}</p>
538
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539 If the macro was defined in a different template you have to
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540 :ref:`import <import>` it first.
541
542 Inside macros you have access to three special variables:
543
544 `varargs`
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545 If more positional arguments are passed to the macro than accepted by the
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546 macro they end up in the special `varargs` variable as list of values.
547
548 `kwargs`
549 Like `varargs` but for keyword arguments. All unconsumed keyword
550 arguments are stored in this special variable.
551
552 `caller`
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553 If the macro was called from a :ref:`call<call>` tag the caller is stored
554 in this variable as macro which can be called.
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555
556 Macros also expose some of their internal details. The following attributes
557 are available on a macro object:
558
559 `name`
560 The name of the macro. ``{{ input.name }}`` will print ``input``.
561
562 `arguments`
563 A tuple of the names of arguments the macro accepts.
564
565 `defaults`
566 A tuple of default values.
567
568 `catch_kwargs`
569 This is `true` if the macro accepts extra keyword arguments (ie: accesses
570 the special `kwargs` variable).
571
572 `catch_varargs`
573 This is `true` if the macro accepts extra positional arguments (ie:
574 accesses the special `varargs` variable).
575
576 `caller`
577 This is `true` if the macro accesses the special `caller` variable and may
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578 be called from a :ref:`call<call>` tag.
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579
580
581 .. _call:
582
583 Call
584 ~~~~
585
586 In some cases it can be useful to pass a macro to another macro. For this
587 purpose you can use the special `call` block. The following example shows
588 a macro that takes advantage of the call functionality and how it can be
589 used::
590
591 {% macro render_dialog(title, class='dialog') -%}
592 <div class="{{ class }}">
593 <h2>{{ title }}</h2>
594 <div class="contents">
595 {{ caller() }}
596 </div>
597 </div>
598 {%- endmacro %}
599
600 {% call render_dialog('Hello World') %}
601 This is a simple dialog rendered by using a macro and
602 a call block.
603 {% endcall %}
604
605 It's also possible to pass arguments back to the call block. This makes it
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606 useful as replacement for loops. Generally speaking a call block works
607 exactly like an macro, just that it doesn't have a name.
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608
609 Here an example of how a call block can be used with arguments::
610
611 {% macro dump_users(users) -%}
612 <ul>
613 {%- for user in users %}
614 <li><p>{{ user.username|e }}</p>{{ caller(user) }}</li>
615 {%- endfor %}
616 </ul>
617 {%- endmacro %}
618
619 {% call(user) dump_users(list_of_user) %}
620 <dl>
621 <dl>Realname</dl>
622 <dd>{{ user.realname|e }}</dd>
623 <dl>Description</dl>
624 <dd>{{ user.description }}</dd>
625 </dl>
626 {% endcall %}
627
628
629 Assignments
630 ~~~~~~~~~~~
631
632 Inside code blocks you can also assign values to variables. Assignments at
633 top level (outside of blocks, macros or loops) are exported from the template
634 like top level macros and can be imported by other templates.
635
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636 Assignments use the `set` tag and can have multiple targets::
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637
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638 {% set navigation = [('index.html', 'Index'), ('about.html', 'About')] %}
639 {% set key, value = call_something() %}
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640
641
642 Extends
643 ~~~~~~~
644
645 The `extends` tag can be used to extend a template from another one. You
646 can have multiple of them in a file but only one of them may be executed
647 at the time. There is no support for multiple inheritance. See the section
648 about :ref:`template-inheritance` above.
649
650
651 Block
652 ~~~~~
653
654 Blocks are used for inheritance and act as placeholders and replacements
655 at the same time. They are documented in detail as part of the section
656 about :ref:`template-inheritance`.
657
658
659 Include
660 ~~~~~~~
661
662 The `include` statement is useful to include a template and return the
663 rendered contents of that file into the current namespace::
664
665 {% include 'header.html' %}
666 Body
667 {% include 'footer.html' %}
668
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669 Included templates have access to the variables of the active context by
670 default. For more details about context behavior of imports and includes
671 see :ref:`import-visibility`.
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672
673 .. _import:
674
675 Import
676 ~~~~~~
677
678 Jinja2 supports putting often used code into macros. These macros can go into
679 different templates and get imported from there. This works similar to the
680 import statements in Python. It's important to know that imports are cached
681 and imported templates don't have access to the current template variables,
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682 just the globals by defualt. For more details about context behavior of
683 imports and includes see :ref:`import-visibility`.
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684
685 There are two ways to import templates. You can import the complete template
686 into a variable or request specific macros / exported variables from it.
687
688 Imagine we have a helper module that renders forms (called `forms.html`)::
689
690 {% macro input(name, value='', type='text') -%}
691 <input type="{{ type }}" value="{{ value|e }}" name="{{ name }}">
692 {%- endmacro %}
693
694 {%- macro textarea(name, value='', rows=10, cols=40) -%}
695 <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
696 }}">{{ value|e }}</textarea>
697 {%- endmacro %}
698
699 The easiest and most flexible is importing the whole module into a variable.
700 That way you can access the attributes::
701
702 {% import 'forms.html' as forms %}
703 <dl>
704 <dt>Username</dt>
705 <dd>{{ forms.input('username') }}</dd>
706 <dt>Password</dt>
707 <dd>{{ forms.input('password', type='password') }}</dd>
708 </dl>
709 <p>{{ forms.textarea('comment') }}</p>
710
711
712 Alternatively you can import names from the template into the current
713 namespace::
714
715 {% from 'forms.html' import input as input_field, textarea %}
716 <dl>
717 <dt>Username</dt>
718 <dd>{{ input_field('username') }}</dd>
719 <dt>Password</dt>
720 <dd>{{ input_field('password', type='password') }}</dd>
721 </dl>
722 <p>{{ textarea('comment') }}</p>
723
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724 Macros and variables starting with one ore more underscores are private and
725 cannot be imported.
726
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727
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728 .. _import-visibility:
729
730 Import Context Behavior
731 -----------------------
732
733 Per default included templates are passed the current context and imported
734 templates not. The reason for this is that imports unlike includes are
735 cached as imports are often used just as a module that holds macros.
736
737 This however can be changed of course explicitly. By adding `with context`
738 or `without context` to the import/include directive the current context
739 can be passed to the template and caching is disabled automatically.
740
741 Here two examples::
742
743 {% from 'forms.html' import input with context %}
744 {% include 'header.html' without context %}
745
746
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747 .. _expressions:
748
749 Expressions
750 -----------
751
752 Jinja allows basic expressions everywhere. These work very similar to regular
753 Python and even if you're not working with Python you should feel comfortable
754 with it.
755
756 Literals
757 ~~~~~~~~
758
759 The simplest form of expressions are literals. Literals are representations
760 for Python objects such as strings and numbers. The following literals exist:
761
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762 "Hello World":
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763 Everything between two double or single quotes is a string. They are
764 useful whenever you need a string in the template (for example as
765 arguments to function calls, filters or just to extend or include a
766 template).
767
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768 42 / 42.23:
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769 Integers and floating point numbers are created by just writing the
770 number down. If a dot is present the number is a float, otherwise an
771 integer. Keep in mind that for Python ``42`` and ``42.0`` is something
772 different.
773
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774 ['list', 'of', 'objects']:
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775 Everything between two brackets is a list. Lists are useful to store
776 sequential data in or to iterate over them. For example you can easily
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777 create a list of links using lists and tuples with a for loop::
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778
779 <ul>
780 {% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
781 ('downloads.html', 'Downloads')] %}
782 <li><a href="{{ href }}">{{ caption }}</a></li>
783 {% endfor %}
784 </ul>
785
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786 ('tuple', 'of', 'values'):
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787 Tuples are like lists, just that you can't modify them. If the tuple
788 only has one item you have to end it with a comma. Tuples are usually
789 used to represent items of two or more elements. See the example above
790 for more details.
791
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792 {'dict': 'of', 'key': 'and', 'value': 'pairs'}:
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793 A dict in Python is a structure that combines keys and values. Keys must
794 be unique and always have exactly one value. Dicts are rarely used in
795 templates, they are useful in some rare cases such as the :func:`xmlattr`
796 filter.
797
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798 true / false:
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799 true is always true and false is always false. Keep in mind that those
800 literals are lowercase!
801
802 Math
803 ~~~~
804
805 Jinja allows you to calculate with values. This is rarely useful in templates
806 but exists for completeness sake. The following operators are supported:
807
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808 \+
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809 Adds two objects with each other. Usually numbers but if both objects are
810 strings or lists you can concatenate them this way. This however is not
811 the preferred way to concatenate strings! For string concatenation have
812 a look at the ``~`` operator. ``{{ 1 + 1 }}`` is ``2``.
813
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814 \-
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815 Substract two numbers from each other. ``{{ 3 - 2 }}`` is ``1``.
816
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817 /
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818 Divide two numbers. The return value will be a floating point number.
819 ``{{ 1 / 2 }}`` is ``{{ 0.5 }}``.
820
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821 //
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822 Divide two numbers and return the truncated integer result.
823 ``{{ 20 / 7 }}`` is ``2``.
824
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825 %
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826 Calculate the remainder of an integer division between the left and right
827 operand. ``{{ 11 % 7 }}`` is ``4``.
828
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829 \*
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830 Multiply the left operand with the right one. ``{{ 2 * 2 }}`` would
831 return ``4``. This can also be used to repeat string multiple times.
832 ``{{ '=' * 80 }}`` would print a bar of 80 equal signs.
833
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834 \**
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835 Raise the left operand to the power of the right operand. ``{{ 2**3 }}``
836 would return ``8``.
837
838 Logic
839 ~~~~~
840
841 For `if` statements / `for` filtering or `if` expressions it can be useful to
842 combine group multiple expressions:
843
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844 and
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845 Return true if the left and the right operand is true.
846
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847 or
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848 Return true if the left or the right operand is true.
849
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850 not
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851 negate a statement (see below).
852
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853 (expr)
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854 group an expression.
855
856 Note that there is no support for any bit operations or something similar.
857
858 - special note regarding ``not``: The ``is`` and ``in`` operators support
859 negation using an infix notation too: ``foo is not bar`` and
860 ``foo not in bar`` instead of ``not foo is bar`` and ``not foo in bar``.
861 All other expressions require a prefix notation: ``not (foo and bar).``
862
863
864 Other Operators
865 ~~~~~~~~~~~~~~~
866
867 The following operators are very useful but don't fit into any of the other
868 two categories:
869
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870 in
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871 Perform sequence / mapping containment test. Returns true if the left
872 operand is contained in the right. ``{{ 1 in [1, 2, 3] }}`` would for
873 example return true.
874
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875 is
876 Performs a :ref:`test <tests>`.
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877
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878 \|
879 Applies a :ref:`filter <filters>`.
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880
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881 ~
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882 Converts all operands into strings and concatenates them.
883 ``{{ "Hello " ~ name ~ "!" }}`` would return (assuming `name` is
884 ``'John'``) ``Hello John!``.
885
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886 ()
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887 Call a callable: ``{{ post.render() }}``. Inside of the parentheses you
888 can use arguments and keyword arguments like in python:
889 ``{{ post.render(user, full=true) }}``.
890
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891 . / []
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892 Get an attribute of an object. (See :ref:`variables`)
893
894
895 .. _if-expression:
896
897 If Expression
898 ~~~~~~~~~~~~~
899
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900 It is also possible to use inline `if` expressions. These are useful in some
901 situations. For example you can use this to extend from one template if a
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902 variable is defined, otherwise from the default layout template::
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903
904 {% extends layout_template if layout_template is defined else 'master.html' %}
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905
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906 The general syntax is ``<do something> if <something is true> else <do
907 something else>``.
908
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909
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910 .. _builtin-filters:
911
912 List of Builtin Filters
913 -----------------------
914
915 .. jinjafilters::
916
917
918 .. _builtin-tests:
919
920 List of Builtin Tests
921 ---------------------
922
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923 .. jinjatests::
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924
925
926 List of Global Functions
927 ------------------------
928
929 The following functions are available in the global scope by default:
930
931 .. function:: range([start,] stop[, step])
932
933 Return a list containing an arithmetic progression of integers.
934 range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
935 When step is given, it specifies the increment (or decrement).
936 For example, range(4) returns [0, 1, 2, 3]. The end point is omitted!
937 These are exactly the valid indices for a list of 4 elements.
938
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939 This is useful to repeat a template block multiple times for example
940 to fill a list. Imagine you have 7 users in the list but you want to
941 render three empty items to enforce a height with CSS::
942
943 <ul>
944 {% for user in users %}
945 <li>{{ user.username }}</li>
946 {% endfor %}
947 {% for number in range(10 - users|count) %}
948 <li class="empty"><span>...</span></li>
949 {% endfor %}
950 </ul>
951
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952 .. function:: lipsum(n=5, html=True, min=20, max=100)
953
954 Generates some lorem ipsum for the template. Per default five paragraphs
955 with HTML are generated each paragraph between 20 and 100 words. If html
956 is disabled regular text is returned. This is useful to generate simple
957 contents for layout testing.
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958
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959 .. function:: dict(\**items)
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960
961 A convenient alternative to dict literals. ``{'foo': 'bar'}`` is the same
962 as ``dict(foo='bar')``.
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963
964
965 Extensions
966 ----------
967
968 The following sections cover the built-in Jinja2 extensions that may be
969 enabled by the application. The application could also provide further
970 extensions not covered by this documentation. In that case there should
971 be a separate document explaining the extensions.
972
973 .. _i18n-in-templates:
974
975 i18n
976 ~~~~
977
978 If the i18n extension is enabled it's possible to mark parts in the template
979 as translatable. To mark a section as translatable you can use `trans`::
980
981 <p>{% trans %}Hello {{ user }}!{% endtrans %}</p>
982
983 To translate a template expression --- say, using template filters or just
984 accessing an attribute of an object --- you need to bind the expression to a
985 name for use within the translation block::
986
987 <p>{% trans user=user.username %}Hello {{ user }}!{% endtrans %}</p>
988
989 If you need to bind more than one expression inside a `trans` tag, separate
990 the pieces with a comma (``,``)::
991
992 {% trans book_title=book.title, author=author.name %}
993 This is {{ book_title }} by {{ author }}
994 {% endtrans %}
995
996 Inside trans tags no statements are allowed, only variable tags are.
997
998 To pluralize, specify both the singular and plural forms with the `pluralize`
999 tag, which appears between `trans` and `endtrans`::
1000
1001 {% trans count=list|length %}
1002 There is {{ count }} {{ name }} object.
1003 {% pluralize %}
1004 There are {{ count }} {{ name }} objects.
1005 {% endtrans %}
1006
1007 Per default the first variable in a block is used to determine the correct
1008 singular or plural form. If that doesn't work out you can specify the name
1009 which should be used for pluralizing by adding it as parameter to `pluralize`::
1010
1011 {% trans ..., user_count=users|length %}...
1012 {% pluralize user_count %}...{% endtrans %}
1013
1014 It's also possible to translate strings in expressions. For that purpose
1015 three functions exist:
1016
1017 _ `gettext`: translate a single string
1018 - `ngettext`: translate a pluralizable string
1019 - `_`: alias for `gettext`
1020
1021 For example you can print a translated string easily this way::
1022
1023 {{ _('Hello World!') }}
1024
1025 To use placeholders you can use the `format` filter::
1026
1027 {{ _('Hello %(user)s!')|format(user=user.username) }}
1028 or
1029 {{ _('Hello %s')|format(user.username) }}
1030
1031 For multiple placeholders always use keyword arguments to `format` as other
1032 languages may not use the words in the same order.
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1033
1034
1035 do
1036 ~~
1037
1038 If the expression-statement extension is loaded a tag called `do` is available
1039 that works exactly like the regular variable expression (``{{ ... }}``) just
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1040 that it doesn't print anything. This can be used to modify lists::
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1041
1042 {% do navigation.append('a string') %}
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1043
1044
1045 Loop Controls
1046 ~~~~~~~~~~~~~
1047
1048 If the application enables the :ref:`loopcontrols-extension` it's possible to
1049 use `break` and `continue` in loops. When `break` is reached, the loop is
1050 terminated, if `continue` is eached the processing is stopped and continues
1051 with the next iteration.
1052
1053 Here a loop that skips every second item::
1054
1055 {% for user in users %}
1056 {%- if loop.index is even %}{% continue %}{% endif %}
1057 ...
1058 {% endfor %}
1059
1060 Likewise a look that stops processing after the 10th iteration::
1061
1062 {% for user in users %}
1063 {%- if loop.index >= 10 %}{% break %}{% endif %}
1064 {%- endfor %}
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