发布于 2015-09-03 10:18:33 | 270 次阅读 | 评论: 0 | 来源: 网络整理
Jinja2 支持扩展来添加过滤器、测试、全局变量或者甚至是处理器。扩展的主要动力是 把诸如添加国际化支持的常用代码迁移到一个可重用的类。
扩展在 Jinja2 环境创建时被添加。一旦环境被创建，就不能添加额外的扩展。要添加 一个扩展，传递一个扩展类或导入路径的列表到 Environment 构造函数的 environment 参数。下面的例子创建了一个加载了 i18n 扩展的 Jinja2 环境:
jinja_env = Environment(extensions=['jinja2.ext.i18n'])
Import name: jinja2.ext.i18n
Jinja2 当前只附带一个扩展，就是 i18n 扩展。它可以与 gettext 或 babel 联合使用。如果启用了 i18n 扩展， Jinja2 提供了 trans 语句来标记被其包裹的 字符串为可翻译的，并调用 gettext 。
在启用虚拟的 _ 函数后，之后的 gettext 调用会被添加到环境的全局变量。那么 一个国际化的应用应该不仅在全局，以及在每次渲染中在命名空间中提供至少一个 gettext 或可选的 ngettext 函数。
在启用这个扩展后，环境提供下面的额外方法:
在该环境中全局安装翻译。提供的翻译对象要至少实现 uggettext 和 ungettext 。 gettext.NullTranslations 和 gettext.GNUTranslations 类和 Babel‘s 的 Translations 类也被支持。
Changed in version 2.5: 添加了新样式的 gettext
安装虚拟的 gettext 函数。这在你想使应用为国际化做准备但还不想实现完整的 国际化系统时很有用。
Changed in version 2.5: 添加了新样式的 gettext
在环境中把给出的 gettext 和 ngettext 可调用量安装为全局变量。它们 应该表现得几乎与标准库中的 gettext.ugettext() 和 gettext.ungettext() 函数相同。
如果激活了 新样式 ，可调用量被包装为新样式的可调用量一样工作。更多 信息见 新样式 Gettext 。
New in version 2.5.
再次卸载翻译。
从给定的模板或源中提取本地化字符串。
对找到的每一个字符串，这个函数生产一个 (lineno, function, message ) 元组，在这里:
对于一个对多种语言可用而对所有用户给出同一种的语言的 web 应用（例如一个法国社 区安全了一个多种语言的论坛软件）可能会一次性加载翻译并且在环境生成时把翻译方 法添加到环境上:
translations = get_gettext_translations()
env = Environment(extensions=['jinja2.ext.i18n'])
env.install_gettext_translations(translations)
get_get_translations 函数会返回当前配置的翻译器。（比如使用 gettext.find ）
模板设计者的 i18n 扩展使用在 模板文档 中有描述。
New in version 2.5.
从版本 2.5 开始你可以使用新样式的 gettext 调用。这些的启发源于 trac 的内部 gettext 函数并且完全被 babel 抽取工具支持。如果你不使用 Babel 的抽取工具， 它可能不会像其它抽取工具预期的那样工作。
标准 gettext 调用和新样式的 gettext 调用有什么区别？通常，它们要输入的东西 更少，出错率更低。并且如果在自动转义环境中使用它们，它们也能更好地支持自动 转义。这里是一些新老样式调用的差异:
标准 gettext:
{{ gettext('Hello World!') }}
{{ gettext('Hello %(name)s!')|format(name='World') }}
{{ ngettext('%(num)d apple', '%(num)d apples', apples|count)|format(
num=apples|count
)}}
新样式看起来是这样:
{{ gettext('Hello World!') }}
{{ gettext('Hello %(name)s!', name='World') }}
{{ ngettext('%(num)d apple', '%(num)d apples', apples|count) }}
新样式 gettext 的优势是你需要输入的更少，并且命名占位符是强制的。后者看起 来似乎是缺陷，但解决了当翻译者不能切换两个占位符的位置时经常勉励的一大堆 麻烦。使用新样式的 gettext ，所有的格式化字符串看起来都一样。
除此之外，在新样式 gettext 中，如果没有使用占位符，字符串格式化也会被使用， 这使得所有的字符串表现一致。最后，不仅是新样式的 gettext 调用可以妥善地为 解决了许多转义相关问题的自动转义标记字符串，许多模板也在使用自动转义时体验 了多次。
Import name: jinja2.ext.loopcontrols
这个扩展添加了循环中的 break 和 continue 支持。在启用它之后， Jinja2 提供的这两个关键字如同 Python 中那样工作。
Import name: jinja2.ext.with_
New in version 2.3.
这个扩展添加了 with 关键字支持。使用这个关键字可以在模板中强制一块嵌套的 作用域。变量可以在 with 语句的块头中直接声明，或直接在里面使用标准的 set 语句。
Import name: jinja2.ext.autoescape
New in version 2.4.
自动转义扩展允许你在模板内开关自动转义特性。如果环境的 autoescape 设定为 False ，它可以被激活。如果是 True 可以被关闭。这个设定的覆盖是有作用域的。
你可以编写扩展来向 Jinja2 中添加自定义标签。这是一个不平凡的任务，而且通常不需 要，因为默认的标签和表达式涵盖了所有常用情况。如 i18n 扩展是一个扩展有用的好例 子，而另一个会是碎片缓存。
当你编写扩展时，你需要记住你在与 Jinja2 模板编译器一同工作，而它并不验证你传递 到它的节点树。如果 AST 是畸形的，你会得到各种各样的编译器或运行时错误，这调试起 来极其可怕。始终确保你在使用创建正确的节点。下面的 API 文档展示了有什么节点和如 何使用它们。
下面的例子用 Werkzeug 的缓存 contrib 模块为 Jinja2 实现了一个 cache 标签:
from jinja2 import nodes
from jinja2.ext import Extension
class FragmentCacheExtension(Extension):
# a set of names that trigger the extension.
tags = set(['cache'])
def __init__(self, environment):
super(FragmentCacheExtension, self).__init__(environment)
# add the defaults to the environment
environment.extend(
fragment_cache_prefix='',
fragment_cache=None
)
def parse(self, parser):
# the first token is the token that started the tag. In our case
# we only listen to ``'cache'`` so this will be a name token with
# `cache` as value. We get the line number so that we can give
# that line number to the nodes we create by hand.
lineno = parser.stream.next().lineno
# now we parse a single expression that is used as cache key.
args = [parser.parse_expression()]
# if there is a comma, the user provided a timeout. If not use
# None as second parameter.
if parser.stream.skip_if('comma'):
args.append(parser.parse_expression())
else:
args.append(nodes.Const(None))
# now we parse the body of the cache block up to `endcache` and
# drop the needle (which would always be `endcache` in that case)
body = parser.parse_statements(['name:endcache'], drop_needle=True)
# now return a `CallBlock` node that calls our _cache_support
# helper method on this extension.
return nodes.CallBlock(self.call_method('_cache_support', args),
[], [], body).set_lineno(lineno)
def _cache_support(self, name, timeout, caller):
"""Helper callback."""
key = self.environment.fragment_cache_prefix + name
# try to load the block from the cache
# if there is no fragment in the cache, render it and store
# it in the cache.
rv = self.environment.fragment_cache.get(key)
if rv is not None:
return rv
rv = caller()
self.environment.fragment_cache.add(key, rv, timeout)
return rv
而这是你在环境中使用它的方式:
from jinja2 import Environment
from werkzeug.contrib.cache import SimpleCache
env = Environment(extensions=[FragmentCacheExtension])
env.fragment_cache = SimpleCache()
之后，在模板中可以标记块为可缓存的。下面的例子缓存一个边栏 300 秒:
{% cache 'sidebar', 300 %}
<div class="sidebar">
...
</div>
{% endcache %}
扩展总是继承 jinja2.ext.Extension 类:
Extensions can be used to add extra functionality to the Jinja template system at the parser level. Custom extensions are bound to an environment but may not store environment specific data on self. The reason for this is that an extension can be bound to another environment (for overlays) by creating a copy and reassigning the environment attribute.
As extensions are created by the environment they cannot accept any arguments for configuration. One may want to work around that by using a factory function, but that is not possible as extensions are identified by their import name. The correct way to configure the extension is storing the configuration values on the environment. Because this way the environment ends up acting as central configuration storage the attributes may clash which is why extensions have to ensure that the names they choose for configuration are not too generic. prefix for example is a terrible name, fragment_cache_prefix on the other hand is a good name as includes the name of the extension (fragment cache).
扩展的标识符。这始终是扩展类的真实导入名，不能被修改。
如果扩展实现自定义标签，这是扩展监听的标签名的集合。
Return an attribute node for the current extension. This is useful to pass constants on extensions to generated template code.
self.attr('_my_attribute', lineno=lineno)
Call a method of the extension. This is a shortcut for attr() + jinja2.nodes.Call.
It’s passed a TokenStream that can be used to filter tokens returned. This method has to return an iterable of Tokens, but it doesn’t have to return a TokenStream.
In the ext folder of the Jinja2 source distribution there is a file called inlinegettext.py which implements a filter that utilizes this method.
If any of the tags matched this method is called with the parser as first argument. The token the parser stream is pointing at is the name token that matched. This method has to return one or a list of multiple nodes.
This method is called before the actual lexing and can be used to preprocess the source. The filename is optional. The return value must be the preprocessed source.
传递到 Extension.parse() 的解析器提供解析不同类型表达式的方式。下 面的方法可能会在扩展中使用:
This is the central parsing class Jinja2 uses. It’s passed to extensions and can be used to parse expressions or statements.
模板的加载名。
当前的 TokenStream 。
Convenience method that raises exc with the message, passed line number or last line number as well as the current name and filename.
Return a new free identifier as InternalName.
Parse an assignment target. As Jinja2 allows assignments to tuples, this function can parse all allowed assignment targets. Per default assignments to tuples are parsed, that can be disable however by setting with_tuple to False. If only assignments to names are wanted name_only can be set to True. The extra_end_rules parameter is forwarded to the tuple parsing function.
Parse an expression. Per default all expressions are parsed, if the optional with_condexpr parameter is set to False conditional expressions are not parsed.
Parse multiple statements into a list until one of the end tokens is reached. This is used to parse the body of statements as it also parses template data if appropriate. The parser checks first if the current token is a colon and skips it if there is one. Then it checks for the block end and parses until if one of the end_tokens is reached. Per default the active token in the stream at the end of the call is the matched end token. If this is not wanted drop_needle can be set to True and the end token is removed.
Works like parse_expression but if multiple expressions are delimited by a comma a Tuple node is created. This method could also return a regular expression instead of a tuple if no commas where found.
The default parsing mode is a full tuple. If simplified is True only names and literals are parsed. The no_condexpr parameter is forwarded to parse_expression().
Because tuples do not require delimiters and may end in a bogus comma an extra hint is needed that marks the end of a tuple. For example for loops support tuples between for and in. In that case the extra_end_rules is set to ['name:in'].
explicit_parentheses is true if the parsing was triggered by an expression in parentheses. This is used to figure out if an empty tuple is a valid expression or not.
A token stream is an iterable that yields Tokens. The parser however does not iterate over it but calls next() to go one token ahead. The current active token is stored as current.
Are we at the end of the stream?
Expect a given token type and return it. This accepts the same argument as jinja2.lexer.Token.test().
Look at the next token.
Go one token ahead and return the old one
Perform the token test and return the token if it matched. Otherwise the return value is None.
Push a token back to the stream.
Got n tokens ahead.
Like next_if() but only returns True or False.
Token class.
token 的行号。
token 的类型。这个值是被禁锢的，所以你可以用 is 运算符同任意字符 串比较。
token 的值。
Test a token against a token expression. This can either be a token type or 'token_type:token_value'. This can only test against string values and types.
Test against multiple token expressions.
同样，在词法分析模块中也有一个实用函数可以计算字符串中的换行符数目:
.. autofunction:: jinja2.lexer.count_newlines
AST（抽象语法树: Abstract Syntax Tree）用于表示解析后的模板。它有编译器之后 转换到可执行的 Python 代码对象的节点构建。提供自定义语句的扩展可以返回执行自 定义 Python 代码的节点。
下面的清单展示了所有当前可用的节点。 AST 在 Jinja2 的各个版本中有差异，但会向 后兼容。
更多信息请见 jinja2.Environment.parse() 。
Baseclass for all Jinja2 nodes. There are a number of nodes available of different types. There are four major types:
All nodes have fields and attributes. Fields may be other nodes, lists, or arbitrary values. Fields are passed to the constructor as regular positional arguments, attributes as keyword arguments. Each node has two attributes: lineno (the line number of the node) and environment. The environment attribute is set at the end of the parsing process for all nodes automatically.
Find the first node of a given type. If no such node exists the return value is None.
Find all the nodes of a given type. If the type is a tuple, the check is performed for any of the tuple items.
Iterates over all direct child nodes of the node. This iterates over all fields and yields the values of they are nodes. If the value of a field is a list all the nodes in that list are returned.
This method iterates over all fields that are defined and yields (key, value) tuples. Per default all fields are returned, but it’s possible to limit that to some fields by providing the only parameter or to exclude some using the exclude parameter. Both should be sets or tuples of field names.
Reset the context of a node and all child nodes. Per default the parser will all generate nodes that have a ‘load’ context as it’s the most common one. This method is used in the parser to set assignment targets and other nodes to a store context.
Set the environment for all nodes.
Set the line numbers of the node and children.
Baseclass for all expressions.
| Node type: | Node |
|---|
Return the value of the expression as constant or raise Impossible if this was not possible.
An EvalContext can be provided, if none is given a default context is created which requires the nodes to have an attached environment.
Changed in version 2.4: the eval_ctx parameter was added.
Check if it’s possible to assign something to this node.
Divides the left by the right node and truncates conver the result into an integer by truncating.
| Node type: | BinExpr |
|---|
Calls an expression. args is a list of arguments, kwargs a list of keyword arguments (list of Keyword nodes), and dyn_args and dyn_kwargs has to be either None or a node that is used as node for dynamic positional (*args) or keyword (**kwargs) arguments.
| Node type: | Expr |
|---|
Compares an expression with some other expressions. ops must be a list of Operands.
| Node type: | Expr |
|---|
Concatenates the list of expressions provided after converting them to unicode.
| Node type: | Expr |
|---|
A conditional expression (inline if expression). ({{ foo if bar else baz }})
| Node type: | Expr |
|---|
Returns the current template context. It can be used like a Name node, with a 'load' ctx and will return the current Context object.
Here an example that assigns the current template name to a variable named foo:
Assign(Name('foo', ctx='store'),
Getattr(ContextReference(), 'name'))
| Node type: | Expr |
|---|
Loads an attribute from the environment object. This is useful for extensions that want to call a callback stored on the environment.
| Node type: | Expr |
|---|
Returns the attribute of an extension bound to the environment. The identifier is the identifier of the Extension.
This node is usually constructed by calling the attr() method on an extension.
| Node type: | Expr |
|---|
This node applies a filter on an expression. name is the name of the filter, the rest of the fields are the same as for Call.
If the node of a filter is None the contents of the last buffer are filtered. Buffers are created by macros and filter blocks.
| Node type: | Expr |
|---|
Get an attribute or item from an expression that is a ascii-only bytestring and prefer the attribute.
| Node type: | Expr |
|---|
Get an attribute or item from an expression and prefer the item.
| Node type: | Expr |
|---|
If created with an import name the import name is returned on node access. For example ImportedName('cgi.escape') returns the escape function from the cgi module on evaluation. Imports are optimized by the compiler so there is no need to assign them to local variables.
| Node type: | Expr |
|---|
An internal name in the compiler. You cannot create these nodes yourself but the parser provides a free_identifier() method that creates a new identifier for you. This identifier is not available from the template and is not threated specially by the compiler.
| Node type: | Expr |
|---|
All constant values. The parser will return this node for simple constants such as 42 or "foo" but it can be used to store more complex values such as lists too. Only constants with a safe representation (objects where eval(repr(x)) == x is true).
| Node type: | Literal |
|---|
Any dict literal such as {1: 2, 3: 4}. The items must be a list of Pair nodes.
| Node type: | Literal |
|---|
For loop unpacking and some other things like multiple arguments for subscripts. Like for Name ctx specifies if the tuple is used for loading the names or storing.
| Node type: | Literal |
|---|
Mark the wrapped expression as safe (wrap it as Markup).
| Node type: | Expr |
|---|
Mark the wrapped expression as safe (wrap it as Markup) but only if autoescaping is active.
New in version 2.5.
| Node type: | Expr |
|---|
Looks up a name or stores a value in a name. The ctx of the node can be one of the following values:
| Node type: | Expr |
|---|
Represents a slice object. This must only be used as argument for Subscript.
| Node type: | Expr |
|---|
Applies a test on an expression. name is the name of the test, the rest of the fields are the same as for Call.
| Node type: | Expr |
|---|
Make the expression positive (noop for most expressions)
| Node type: | UnaryExpr |
|---|
A key, value pair for keyword arguments where key is a string.
| Node type: | Helper |
|---|
Holds an operator and an expression. The following operators are available: %, **, *, +, -, //, /, eq, gt, gteq, in, lt, lteq, ne, not, notin
| Node type: | Helper |
|---|
Like a macro without a name but a call instead. call is called with the unnamed macro as caller argument this node holds.
| Node type: | Stmt |
|---|
Modifies the eval context. For each option that should be modified, a Keyword has to be added to the options list.
Example to change the autoescape setting:
EvalContextModifier(options=[Keyword('autoescape', Const(True))])
| Node type: | Stmt |
|---|
Modifies the eval context and reverts it later. Works exactly like EvalContextModifier but will only modify the EvalContext for nodes in the body.
| Node type: | EvalContextModifier |
|---|
A statement that evaluates an expression and discards the result.
| Node type: | Stmt |
|---|
The for loop. target is the target for the iteration (usually a Name or Tuple), iter the iterable. body is a list of nodes that are used as loop-body, and else_ a list of nodes for the else block. If no else node exists it has to be an empty list.
For filtered nodes an expression can be stored as test, otherwise None.
| Node type: | Stmt |
|---|
A node that represents the from import tag. It’s important to not pass unsafe names to the name attribute. The compiler translates the attribute lookups directly into getattr calls and does not use the subscript callback of the interface. As exported variables may not start with double underscores (which the parser asserts) this is not a problem for regular Jinja code, but if this node is used in an extension extra care must be taken.
The list of names may contain tuples if aliases are wanted.
| Node type: | Stmt |
|---|
If test is true, body is rendered, else else_.
| Node type: | Stmt |
|---|
A node that represents the import tag.
| Node type: | Stmt |
|---|
A node that represents the include tag.
| Node type: | Stmt |
|---|
A macro definition. name is the name of the macro, args a list of arguments and defaults a list of defaults if there are any. body is a list of nodes for the macro body.
| Node type: | Stmt |
|---|
A node that holds multiple expressions which are then printed out. This is used both for the print statement and the regular template data.
| Node type: | Stmt |
|---|
Node that represents a template. This must be the outermost node that is passed to the compiler.
| Node type: | Node |
|---|
Raised if the node could not perform a requested action.