jinja2模板设计一：变量、过滤器

模板设计者文档

这份文档描述了模板引擎中的语法和语义结构，对于创建 Jinja 模板是一份相当有用的参考。因为模板引擎非常灵活，应用中的配置会在分隔符和未定义值的行为方面与这里的配置有细微差异。

一、概要

模板仅仅是文本文件。它可以生成任何基于文本的格式（HTML、XML、CSV、LaTex 等等）。它并没有特定的扩展名， .html 或 .xml 都是可以的。

模板包含变量或 表达式 ，这两者在模板求值的时候会被替换为值。模板中还有标签，控制模板的逻辑。模板语法的大量灵感来自于 Django 和 Python 。

下面是一个最小的模板，它阐明了一些基础。我们会在文档中后面的部分解释细节:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
    <title>My Webpage</title>
</head>
<body>
    <ul id="navigation">
    {% for item in navigation %}
        <li><a href="{{ item.href }}">{{ item.caption }}</a></li>
    {% endfor %}
    </ul>

    <h1>My Webpage</h1>
    {{ a_variable }}
</body>
</html>

这包含了默认的设定。应用开发者也会把语法从 {% foo %} 改成 <% foo %> 或类似的东西。

这里有两种分隔符: {% ... %} 和 {{ ... }} 。前者用于执行诸如 for 循环或赋值的语句，后者把表达式的结果打印到模板上。

二、变量

应用把变量传递到模板，你可能在模板中弄混。变量上面也可以有你能访问的属性或元素。变量看起来是什么，完全取决于应用提供了什么。

你可以使用点（ . ）来访问变量的属性，作为替代，也可以使用所谓的“下标”语法（ []）。下面的几行效果是一样的:

{{ foo.bar }}
{{ foo['bar'] }}

知晓花括号不是变量的一部分，而是打印语句的一部分是重要的。如果你访问标签里的不带括号的变量。

如果变量或属性不存在，会返回一个未定义值。你可以对这类值做什么取决于应用的配置，默认的行为是它如果被打印，其求值为一个空字符串，并且你可以迭代它，但其它操作会失败。

实现：

为方便起见，Jinja2 中 foo.bar 在 Python 层中做下面的事情:

检查 foo 上是否有一个名为 bar 的属性。
如果没有，检查 foo 中是否有一个 'bar' 项。
如果没有，返回一个未定义对象。

foo['bar'] 的方式相反，只在顺序上有细小差异:

检查在 foo 中是否有一个 'bar' 项。
如果没有，检查 foo 上是否有一个名为 bar 的属性。
如果没有，返回一个未定义对象。

如果一个对象有同名的项和属性，这很重要。此外，有一个 attr() 过滤器，它只查找属性。

三、过滤器

变量可以通过 过滤器 修改。过滤器与变量用管道符号（ | ）分割，并且也可以用圆括号传递可选参数。多个过滤器可以链式调用，前一个过滤器的输出会被作为后一个过滤器的输入。

例如 {{ name|striptags|title }} 会移除 name 中的所有 HTML 标签并且改写为标题样式的大小写格式。

过滤器接受带圆括号的参数，如同函数调用。这个例子会把一个列表用逗号连接起来: {{ list|join(', ') }} 。

内置过滤器清单

abs(number): Return the absolute value of the argument.

attr(obj, name)

Get an attribute of an object. foo|attr("bar") works like foo["bar"] just that always an attribute is returned and items are not looked up.

See Notes on subscriptions for more details.

batch(value, linecount, fill_with=None)

A filter that batches items. It works pretty much like slice just the other way round. It returns a list of lists with the given number of items. If you provide a second parameter this is used to fill up missing items. See this example:

<table>
{%- for row in items|batch(3, '&nbsp;') %}
  <tr>
  {%- for column in row %}
    <td>{{ column }}</td>
  {%- endfor %}
  </tr>
{%- endfor %}
</table>

capitalize(s): Capitalize a value. The first character will be uppercase, all others lowercase.

center(value, width=80): Centers the value in a field of a given width.

default(value, default_value=u'', boolean=False)

If the value is undefined it will return the passed default value, otherwise the value of the variable:

{{ my_variable|default('my_variable is not defined') }}

This will output the value of my_variable if the variable was defined, otherwise 'my_variable is not defined'. If you want to use default with variables that evaluate to false you have to set the second parameter to true:

{{ ''|default('the string was empty', true) }}

Aliases :	`d`

dictsort(value, case_sensitive=False, by='key')

Sort a dict and yield (key, value) pairs. Because python dicts are unsorted you may want to use this function to order them by either key or value:

{% for item in mydict|dictsort %}
    sort the dict by key, case insensitive

{% for item in mydict|dictsort(true) %}
    sort the dict by key, case sensitive

{% for item in mydict|dictsort(false, 'value') %}
    sort the dict by key, case insensitive, sorted
    normally and ordered by value.

escape(s)

Convert the characters &, <, >, ‘, and ” in string s to HTML-safe sequences. Use this if you need to display text that might contain such characters in HTML. Marks return value as markup string.

Aliases :	`e`

filesizeformat(value, binary=False): Format the value like a ‘human-readable’ file size (i.e. 13 kB, 4.1 MB, 102 Bytes, etc). Per default decimal prefixes are used (Mega, Giga, etc.), if the second parameter is set to True the binary prefixes are used (Mebi, Gibi).

first(seq): Return the first item of a sequence.

float(value, default=0.0): Convert the value into a floating point number. If the conversion doesn’t work it will return 0.0. You can override this default using the first parameter.

forceescape(value): Enforce HTML escaping. This will probably double escape variables.

format(value, *args, **kwargs)

Apply python string formatting on an object:

{{ "%s - %s"|format("Hello?", "Foo!") }}
    -> Hello? - Foo!

groupby(value, attribute)

Group a sequence of objects by a common attribute.

If you for example have a list of dicts or objects that represent persons with gender, first_name and last_name attributes and you want to group all users by genders you can do something like the following snippet:

<ul>
{% for group in persons|groupby('gender') %}
    <li>{{ group.grouper }}<ul>
    {% for person in group.list %}
        <li>{{ person.first_name }} {{ person.last_name }}</li>
    {% endfor %}</ul></li>
{% endfor %}
</ul>

Additionally it’s possible to use tuple unpacking for the grouper and list:

<ul>
{% for grouper, list in persons|groupby('gender') %}
    ...
{% endfor %}
</ul>

As you can see the item we’re grouping by is stored in the grouper attribute and the list contains all the objects that have this grouper in common.

Changed in version 2.6: It’s now possible to use dotted notation to group by the child attribute of another attribute.

indent(s, width=4, indentfirst=False)

Return a copy of the passed string, each line indented by 4 spaces. The first line is not indented. If you want to change the number of spaces or indent the first line too you can pass additional parameters to the filter:

{{ mytext|indent(2, true) }}
    indent by two spaces and indent the first line too.

int(value, default=0): Convert the value into an integer. If the conversion doesn’t work it will return 0. You can override this default using the first parameter.

join(value, d=u'', attribute=None)

Return a string which is the concatenation of the strings in the sequence. The separator between elements is an empty string per default, you can define it with the optional parameter:

{{ [1, 2, 3]|join('|') }}
    -> 1|2|3

{{ [1, 2, 3]|join }}
    -> 123

It is also possible to join certain attributes of an object:

{{ users|join(', ', attribute='username') }}

New in version 2.6: The attribute parameter was added.

last(seq): Return the last item of a sequence.

length(object)

Return the number of items of a sequence or mapping.

Aliases :	`count`

list(value): Convert the value into a list. If it was a string the returned list will be a list of characters.

lower(s): Convert a value to lowercase.

map()

Applies a filter on a sequence of objects or looks up an attribute. This is useful when dealing with lists of objects but you are really only interested in a certain value of it.

The basic usage is mapping on an attribute. Imagine you have a list of users but you are only interested in a list of usernames:

Users on this page: {{ users|map(attribute='username')|join(', ') }}

Alternatively you can let it invoke a filter by passing the name of the filter and the arguments afterwards. A good example would be applying a text conversion filter on a sequence:

Users on this page: {{ titles|map('lower')|join(', ') }}

New in version 2.7.

pprint(value, verbose=False)

Pretty print a variable. Useful for debugging.

With Jinja 1.2 onwards you can pass it a parameter. If this parameter is truthy the output will be more verbose (this requires pretty)

random(seq): Return a random item from the sequence.

reject()

Filters a sequence of objects by appying a test to either the object or the attribute and rejecting the ones with the test succeeding.

Example usage:

{{ numbers|reject("odd") }}

New in version 2.7.

rejectattr()

Filters a sequence of objects by appying a test to either the object or the attribute and rejecting the ones with the test succeeding.

{{ users|rejectattr("is_active") }}
{{ users|rejectattr("email", "none") }}

New in version 2.7.

replace(s, old, new, count=None)

Return a copy of the value with all occurrences of a substring replaced with a new one. The first argument is the substring that should be replaced, the second is the replacement string. If the optional third argument count is given, only the firstcount occurrences are replaced:

{{ "Hello World"|replace("Hello", "Goodbye") }}
    -> Goodbye World

{{ "aaaaargh"|replace("a", "d'oh, ", 2) }}
    -> d'oh, d'oh, aaargh

reverse(value): Reverse the object or return an iterator the iterates over it the other way round.

round(value, precision=0, method='common')

Round the number to a given precision. The first parameter specifies the precision (default is 0), the second the rounding method:

'common' rounds either up or down
'ceil' always rounds up
'floor' always rounds down

If you don’t specify a method 'common' is used.

{{ 42.55|round }}
    -> 43.0
{{ 42.55|round(1, 'floor') }}
    -> 42.5

Note that even if rounded to 0 precision, a float is returned. If you need a real integer, pipe it through int:

{{ 42.55|round|int }}
    -> 43

safe(value): Mark the value as safe which means that in an environment with automatic escaping enabled this variable will not be escaped.

select()

Filters a sequence of objects by appying a test to either the object or the attribute and only selecting the ones with the test succeeding.

Example usage:

{{ numbers|select("odd") }}

New in version 2.7.

selectattr()

Filters a sequence of objects by appying a test to either the object or the attribute and only selecting the ones with the test succeeding.

Example usage:

{{ users|selectattr("is_active") }}
{{ users|selectattr("email", "none") }}

New in version 2.7.

slice(value, slices, fill_with=None)

Slice an iterator and return a list of lists containing those items. Useful if you want to create a div containing three ul tags that represent columns:

<div class="columwrapper">
  {%- for column in items|slice(3) %}
    <ul class="column-{{ loop.index }}">
    {%- for item in column %}
      <li>{{ item }}</li>
    {%- endfor %}
    </ul>
  {%- endfor %}
</div>

If you pass it a second argument it’s used to fill missing values on the last iteration.

sort(value, reverse=False, case_sensitive=False, attribute=None)

Sort an iterable. Per default it sorts ascending, if you pass it true as first argument it will reverse the sorting.

If the iterable is made of strings the third parameter can be used to control the case sensitiveness of the comparison which is disabled by default.

{% for item in iterable|sort %}
    ...
{% endfor %}

It is also possible to sort by an attribute (for example to sort by the date of an object) by specifying the attribute parameter:

{% for item in iterable|sort(attribute='date') %}
    ...
{% endfor %}

Changed in version 2.6: The attribute parameter was added.

string(object): Make a string unicode if it isn’t already. That way a markup string is not converted back to unicode.

striptags(value): Strip SGML/XML tags and replace adjacent whitespace by one space.

sum(iterable, attribute=None, start=0)

Returns the sum of a sequence of numbers plus the value of parameter ‘start’ (which defaults to 0). When the sequence is empty it returns start.

It is also possible to sum up only certain attributes:

Total: {{ items|sum(attribute='price') }}

Changed in version 2.6: The attribute parameter was added to allow suming up over attributes. Also the start parameter was moved on to the right.

title(s): Return a titlecased version of the value. I.e. words will start with uppercase letters, all remaining characters are lowercase.

trim(value): Strip leading and trailing whitespace.

truncate(s, length=255, killwords=False, end='...')

Return a truncated copy of the string. The length is specified with the first parameter which defaults to 255. If the second parameter is true the filter will cut the text at length. Otherwise it will discard the last word. If the text was in fact truncated it will append an ellipsis sign ("..."). If you want a different ellipsis sign than "..." you can specify it using the third parameter.

{{ "foo bar"|truncate(5) }}
    -> "foo ..."
{{ "foo bar"|truncate(5, True) }}
    -> "foo b..."

upper(s): Convert a value to uppercase.

urlencode(value): Escape strings for use in URLs (uses UTF-8 encoding). It accepts both dictionaries and regular strings as well as pairwise iterables.

New in version 2.7.

urlize(value, trim_url_limit=None, nofollow=False)

Converts URLs in plain text into clickable links.

If you pass the filter an additional integer it will shorten the urls to that number. Also a third argument exists that makes the urls “nofollow”:

{{ mytext|urlize(40, true) }}
    links are shortened to 40 chars and defined with rel="nofollow"

wordcount(s): Count the words in that string.

wordwrap(s, width=79, break_long_words=True, wrapstring=None): Return a copy of the string passed to the filter wrapped after 79 characters. You can override this default using the first parameter. If you set the second parameter to false Jinja will not split words apart if they are longer than width. By default, the newlines will be the default newlines for the environment, but this can be changed using the wrapstring keyword argument.

New in version 2.7: Added support for the wrapstring parameter.

xmlattr(d, autospace=True)

Create an SGML/XML attribute string based on the items in a dict. All values that are neither none nor undefined are automatically escaped:

<ul{{ {'class': 'my_list', 'missing': none,
        'id': 'list-%d'|format(variable)}|xmlattr }}>
...
</ul>

Results in something like this:

<ul class="my_list" id="list-42">
...
</ul>

As you can see it automatically prepends a space in front of the item if the filter returned something unless the second parameter is false.

参考文档：http://docs.jinkan.org/docs/jinja2/templates.html#builtin-filters

posted on 2015-08-02 16:48 myworldworld 阅读(521) 评论(0) 收藏举报

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jinja2模板设计一：变量、过滤器

模板设计者文档

一、概要

二、变量

三、过滤器

内置过滤器清单

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