实用工具
最后更新于：2022-04-01 04:03:18
这些辅助函数和类在你向 Jinja2 环境中添加自定义过滤器或函数时很有用。
jinja2.environmentfilter(*f*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.environmentfilter "Permalink to this definition")
Decorator for marking evironment dependent filters. The current [Environment](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Environment "jinja2.Environment") is passed to the filter as first argument.
jinja2.contextfilter(*f*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.contextfilter "Permalink to this definition")
Decorator for marking context dependent filters. The current Context will be passed as first argument.
jinja2.evalcontextfilter(*f*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.evalcontextfilter "Permalink to this definition")
Decorator for marking eval-context dependent filters. An eval context object is passed as first argument. For more information about the eval context, see [*求值上下文*](http://docs.jinkan.org/docs/jinja2/api.html#eval-context).
New in version 2.4.
jinja2.environmentfunction(*f*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.environmentfunction "Permalink to this definition")
This decorator can be used to mark a function or method as environment callable. This decorator works exactly like the [contextfunction()](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.contextfunction "jinja2.contextfunction") decorator just that the first argument is the active [Environment](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Environment "jinja2.Environment") and not context.
jinja2.contextfunction(*f*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.contextfunction "Permalink to this definition")
This decorator can be used to mark a function or method context callable. A context callable is passed the active Context as first argument when called from the template. This is useful if a function wants to get access to the context or functions provided on the context object. For example a function that returns a sorted list of template variables the current template exports could look like this:
~~~
@contextfunction
def get_exported_names(context):
return sorted(context.exported_vars)
~~~
jinja2.evalcontextfunction(*f*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.evalcontextfunction "Permalink to this definition")
This decorator can be used to mark a function or method as an eval context callable. This is similar to the [contextfunction()](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.contextfunction "jinja2.contextfunction") but instead of passing the context, an evaluation context object is passed. For more information about the eval context, see[*求值上下文*](http://docs.jinkan.org/docs/jinja2/api.html#eval-context).
New in version 2.4.
jinja2.escape(*s*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.escape "Permalink to this definition")
把字符串 s 中 & 、 、 > 、 ' 和 " 转换为 HTML 安 全的序列。如果你需要在 HTML 中显示可能包含这些字符的文本，可以使用它。这 个函数不会转义对象。这个函数不会转义含有 HTML 表达式比如已转义数据的对象。
返回值是一个 [Markup](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup "jinja2.Markup") 字符串。
jinja2.clear_caches()[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.clear_caches "Permalink to this definition")
Jinja2 keeps internal caches for environments and lexers. These are used so that Jinja2 doesn’t have to recreate environments and lexers all the time. Normally you don’t have to care about that but if you are messuring memory consumption you may want to clean the caches.
jinja2.is_undefined(*obj*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.is_undefined "Permalink to this definition")
Check if the object passed is undefined. This does nothing more than performing an instance check against [Undefined](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Undefined "jinja2.Undefined") but looks nicer. This can be used for custom filters or tests that want to react to undefined variables. For example a custom default filter can look like this:
~~~
def default(var, default=''):
if is_undefined(var):
return default
return var
~~~
*class *jinja2.Markup([*string*])[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup "Permalink to this definition")
Marks a string as being safe for inclusion in HTML/XML output without needing to be escaped. This implements the __html__ interface a couple of frameworks and web applications use. [Markup](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup "jinja2.Markup") is a direct subclass of unicode and provides all the methods of unicode just that it escapes arguments passed and always returnsMarkup.
The escape function returns markup objects so that double escaping can’t happen.
The constructor of the [Markup](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup "jinja2.Markup") class can be used for three different things: When passed an unicode object it’s assumed to be safe, when passed an object with an HTML representation (has an __html__ method) that representation is used, otherwise the object passed is converted into a unicode string and then assumed to be safe:
~~~
>>> Markup("Hello <em>World</em>!")
Markup(u'Hello <em>World</em>!')
>>> class Foo(object):
... def __html__(self):
... return '<a href="#">foo</a>'
...
>>> Markup(Foo())
Markup(u'<a href="#">foo</a>')
~~~
If you want object passed being always treated as unsafe you can use the [escape()](http://docs.jinkan.org/docs/jinja2/templates.html#escape "escape")classmethod to create a [Markup](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup "jinja2.Markup") object:
~~~
>>> Markup.escape("Hello <em>World</em>!")
Markup(u'Hello <em>World</em>!')
~~~
Operations on a markup string are markup aware which means that all arguments are passed through the [escape()](http://docs.jinkan.org/docs/jinja2/templates.html#escape "escape") function:
~~~
>>> em = Markup("<em>%s</em>")
>>> em % "foo & bar"
Markup(u'<em>foo & bar</em>')
>>> strong = Markup("<strong>%(text)s</strong>")
>>> strong % {'text': '<blink>hacker here</blink>'}
Markup(u'<strong><blink>hacker here</blink></strong>')
>>> Markup("<em>Hello</em> ") + "<foo>"
Markup(u'<em>Hello</em> <foo>')
~~~
*classmethod *escape(*s*)[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup.escape "Permalink to this definition")
Escape the string. Works like [escape()](http://docs.jinkan.org/docs/jinja2/templates.html#escape "escape") with the difference that for subclasses of[Markup](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup "jinja2.Markup") this function would return the correct subclass.
striptags()[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup.striptags "Permalink to this definition")
Unescape markup into an text_type string and strip all tags. This also resolves known HTML4 and XHTML entities. Whitespace is normalized to one:
~~~
>>> Markup("Main » <em>About</em>").striptags()
u'Main \xbb About'
~~~
unescape()[](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup.unescape "Permalink to this definition")
Unescape markup again into an text_type string. This also resolves known HTML4 and XHTML entities:
~~~
>>> Markup("Main » <em>About</em>").unescape()
u'Main \xbb <em>About</em>'
~~~
Note
Jinja2 的 [Markup](http://docs.jinkan.org/docs/jinja2/api.html#jinja2.Markup "jinja2.Markup") 类至少与 Pylons 和 Genshi 兼容。预计不久更多模板 引擎和框架会采用__html__ 的概念。