"xml.etree.ElementTree" ---  ElementTree XML API
************************************************

**源代码：** Lib/xml/etree/ElementTree.py

======================================================================

"xml.etree.ElementTree" 模块实现了一个简单高效的API，用于解析和创建XML
数据。

3.3 版更變: This module will use a fast implementation whenever
available.

3.3 版後已棄用: The "xml.etree.cElementTree" module is deprecated.

警告:

  "xml.etree.ElementTree" 模块对于恶意构建的数据是不安全的。如果需要解
  析不可信或未经身份验证的数据，请参见 XML 漏洞 。


教程
====

这是一个使用 "xml.etree.ElementTree" （简称 "ET" ）的简短教程。目标是
演示模块的一些构建块和基本概念。


XML树和元素
-----------

XML是一种固有的分层数据格式，最自然的表示方法是使用树。为此， "ET" 有
两个类： "ElementTree" 将整个XML文档表示为一个树， "Element" 表示该树
中的单个节点。与整个文档的交互（读写文件）通常在 "ElementTree" 级别完
成。与单个XML元素及其子元素的交互是在 "Element" 级别完成的。


解析XML
-------

我们将使用以下XML文档作为本节的示例数据：

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank>1</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank>4</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
       <country name="Panama">
           <rank>68</rank>
           <year>2011</year>
           <gdppc>13600</gdppc>
           <neighbor name="Costa Rica" direction="W"/>
           <neighbor name="Colombia" direction="E"/>
       </country>
   </data>

可以通过从文件中读取来导入此数据：

   import xml.etree.ElementTree as ET
   tree = ET.parse('country_data.xml')
   root = tree.getroot()

或直接从字符串中解析：

   root = ET.fromstring(country_data_as_string)

"fromstring()" 将XML从字符串直接解析为 "Element" ，该元素是已解析树的
根元素。其他解析函数可能会创建一个 "ElementTree" 。确切信息请查阅文档
。

作为 "Element" ， "root" 具有标签和属性字典:

   >>> root.tag
   'data'
   >>> root.attrib
   {}

还有可以迭代的子节点：

   >>> for child in root:
   ...     print(child.tag, child.attrib)
   ...
   country {'name': 'Liechtenstein'}
   country {'name': 'Singapore'}
   country {'name': 'Panama'}

子级是可以嵌套的，我们可以通过索引访问特定的子级节点：

   >>> root[0][1].text
   '2008'

備註:

  并非XML输入的所有元素都将作为解析树的元素结束。目前，此模块跳过输入
  中的任何XML注释、处理指令和文档类型声明。然而，使用这个模块的API而不
  是从XML文本解析构建的树可以包含注释和处理指令，生成XML输出时同样包含
  这些注释和处理指令。可以通过将自定义 "TreeBuilder" 实例传递给
  "XMLParser" 构造函数来访问文档类型声明。


Pull API进行非阻塞解析
----------------------

Most parsing functions provided by this module require the whole
document to be read at once before returning any result.  It is
possible to use an "XMLParser" and feed data into it incrementally,
but it is a push API that calls methods on a callback target, which is
too low-level and inconvenient for most needs.  Sometimes what the
user really wants is to be able to parse XML incrementally, without
blocking operations, while enjoying the convenience of fully
constructed "Element" objects.

The most powerful tool for doing this is "XMLPullParser".  It does not
require a blocking read to obtain the XML data, and is instead fed
with data incrementally with "XMLPullParser.feed()" calls.  To get the
parsed XML elements, call "XMLPullParser.read_events()".  Here is an
example:

   >>> parser = ET.XMLPullParser(['start', 'end'])
   >>> parser.feed('<mytag>sometext')
   >>> list(parser.read_events())
   [('start', <Element 'mytag' at 0x7fa66db2be58>)]
   >>> parser.feed(' more text</mytag>')
   >>> for event, elem in parser.read_events():
   ...     print(event)
   ...     print(elem.tag, 'text=', elem.text)
   ...
   end

The obvious use case is applications that operate in a non-blocking
fashion where the XML data is being received from a socket or read
incrementally from some storage device.  In such cases, blocking reads
are unacceptable.

Because it's so flexible, "XMLPullParser" can be inconvenient to use
for simpler use-cases.  If you don't mind your application blocking on
reading XML data but would still like to have incremental parsing
capabilities, take a look at "iterparse()".  It can be useful when
you're reading a large XML document and don't want to hold it wholly
in memory.


查找感兴趣的元素
----------------

"Element" 有一些很有效的方法，可帮助递归遍历其下的所有子树（包括子级，
子级的子级，等等）。例如 "Element.iter()":

   >>> for neighbor in root.iter('neighbor'):
   ...     print(neighbor.attrib)
   ...
   {'name': 'Austria', 'direction': 'E'}
   {'name': 'Switzerland', 'direction': 'W'}
   {'name': 'Malaysia', 'direction': 'N'}
   {'name': 'Costa Rica', 'direction': 'W'}
   {'name': 'Colombia', 'direction': 'E'}

"Element.findall()" 仅查找当前元素的直接子元素中带有指定标签的元素。
"Element.find()" 找带有特定标签的 *第一个* 子级，然后可以用
"Element.text" 访问元素的文本内容。 "Element.get" 访问元素的属性:

   >>> for country in root.findall('country'):
   ...     rank = country.find('rank').text
   ...     name = country.get('name')
   ...     print(name, rank)
   ...
   Liechtenstein 1
   Singapore 4
   Panama 68

通过使用 XPath ，可以更精确地指定要查找的元素。


修改XML文件
-----------

"ElementTree" 提供了一种构建XML文档并将其写入文件的简单方法。调用
"ElementTree.write()" 方法就可以实现。

创建后可以直接操作 "Element" 对象。例如：使用 "Element.text" 修改文本
字段，使用 "Element.set()" 方法添加和修改属性，以及使用
"Element.append()" 添加新的子元素。

假设我们要为每个国家/地区的中添加一个排名，并在排名元素中添加一个
"updated" 属性：

   >>> for rank in root.iter('rank'):
   ...     new_rank = int(rank.text) + 1
   ...     rank.text = str(new_rank)
   ...     rank.set('updated', 'yes')
   ...
   >>> tree.write('output.xml')

生成的XML现在看起来像这样：

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank updated="yes">2</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank updated="yes">5</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
       <country name="Panama">
           <rank updated="yes">69</rank>
           <year>2011</year>
           <gdppc>13600</gdppc>
           <neighbor name="Costa Rica" direction="W"/>
           <neighbor name="Colombia" direction="E"/>
       </country>
   </data>

可以使用 "Element.remove()" 删除元素。假设我们要删除排名高于50的所有国
家/地区:

   >>> for country in root.findall('country'):
   ...     # using root.findall() to avoid removal during traversal
   ...     rank = int(country.find('rank').text)
   ...     if rank > 50:
   ...         root.remove(country)
   ...
   >>> tree.write('output.xml')

Note that concurrent modification while iterating can lead to
problems, just like when iterating and modifying Python lists or
dicts. Therefore, the example first collects all matching elements
with "root.findall()", and only then iterates over the list of
matches.

生成的XML现在看起来像这样：

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank updated="yes">2</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank updated="yes">5</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
   </data>


构建XML文档
-----------

"SubElement()" 函数还提供了一种便捷方法来为给定元素创建新的子元素:

   >>> a = ET.Element('a')
   >>> b = ET.SubElement(a, 'b')
   >>> c = ET.SubElement(a, 'c')
   >>> d = ET.SubElement(c, 'd')
   >>> ET.dump(a)
   <a><b /><c><d /></c></a>


使用命名空间解析XML
-------------------

If the XML input has namespaces, tags and attributes with prefixes in
the form "prefix:sometag" get expanded to "{uri}sometag" where the
*prefix* is replaced by the full *URI*. Also, if there is a default
namespace, that full URI gets prepended to all of the non-prefixed
tags.

Here is an XML example that incorporates two namespaces, one with the
prefix "fictional" and the other serving as the default namespace:

   <?xml version="1.0"?>
   <actors xmlns:fictional="http://characters.example.com"
           xmlns="http://people.example.com">
       <actor>
           <name>John Cleese</name>
           <fictional:character>Lancelot</fictional:character>
           <fictional:character>Archie Leach</fictional:character>
       </actor>
       <actor>
           <name>Eric Idle</name>
           <fictional:character>Sir Robin</fictional:character>
           <fictional:character>Gunther</fictional:character>
           <fictional:character>Commander Clement</fictional:character>
       </actor>
   </actors>

One way to search and explore this XML example is to manually add the
URI to every tag or attribute in the xpath of a "find()" or
"findall()":

   root = fromstring(xml_text)
   for actor in root.findall('{http://people.example.com}actor'):
       name = actor.find('{http://people.example.com}name')
       print(name.text)
       for char in actor.findall('{http://characters.example.com}character'):
           print(' |-->', char.text)

A better way to search the namespaced XML example is to create a
dictionary with your own prefixes and use those in the search
functions:

   ns = {'real_person': 'http://people.example.com',
         'role': 'http://characters.example.com'}

   for actor in root.findall('real_person:actor', ns):
       name = actor.find('real_person:name', ns)
       print(name.text)
       for char in actor.findall('role:character', ns):
           print(' |-->', char.text)

These two approaches both output:

   John Cleese
    |--> Lancelot
    |--> Archie Leach
   Eric Idle
    |--> Sir Robin
    |--> Gunther
    |--> Commander Clement


其他资源
--------

See http://effbot.org/zone/element-index.htm for tutorials and links
to other docs.


XPath支持
=========

This module provides limited support for XPath expressions for
locating elements in a tree.  The goal is to support a small subset of
the abbreviated syntax; a full XPath engine is outside the scope of
the module.


示例
----

Here's an example that demonstrates some of the XPath capabilities of
the module.  We'll be using the "countrydata" XML document from the
Parsing XML section:

   import xml.etree.ElementTree as ET

   root = ET.fromstring(countrydata)

   # Top-level elements
   root.findall(".")

   # All 'neighbor' grand-children of 'country' children of the top-level
   # elements
   root.findall("./country/neighbor")

   # Nodes with name='Singapore' that have a 'year' child
   root.findall(".//year/..[@name='Singapore']")

   # 'year' nodes that are children of nodes with name='Singapore'
   root.findall(".//*[@name='Singapore']/year")

   # All 'neighbor' nodes that are the second child of their parent
   root.findall(".//neighbor[2]")

For XML with namespaces, use the usual qualified "{namespace}tag"
notation:

   # All dublin-core "title" tags in the document
   root.findall(".//{http://purl.org/dc/elements/1.1/}title")


支持的XPath语法
---------------

+-------------------------+--------------------------------------------------------+
| 语法                    | 含义                                                   |
|=========================|========================================================|
| "tag"                   | Selects all child elements with the given tag. For     |
|                         | example, "spam" selects all child elements named       |
|                         | "spam", and "spam/egg" selects all grandchildren named |
|                         | "egg" in all children named "spam". "{namespace}*"     |
|                         | selects all tags in the given namespace, "{*}spam"     |
|                         | selects tags named "spam" in any (or no) namespace,    |
|                         | and "{}*" only selects tags that are not in a          |
|                         | namespace.  3.8 版更變: Support for star-wildcards was |
|                         | added.                                                 |
+-------------------------+--------------------------------------------------------+
| "*"                     | 选择所有子元素，包括注释和处理说明。例如 "*/egg" 选择  |
|                         | 所有名为 "egg" 的 孙元素。                             |
+-------------------------+--------------------------------------------------------+
| "."                     | 选择当前节点。这在路径的开头非常有用，用于指示它是相对 |
|                         | 路径。                                                 |
+-------------------------+--------------------------------------------------------+
| "//"                    | Selects all subelements, on all levels beneath the     |
|                         | current  element. For example, ".//egg" selects all    |
|                         | "egg" elements in the entire tree.                     |
+-------------------------+--------------------------------------------------------+
| ".."                    | Selects the parent element.  Returns "None" if the     |
|                         | path attempts to reach the ancestors of the start      |
|                         | element (the element "find" was called on).            |
+-------------------------+--------------------------------------------------------+
| "[@attrib]"             | 选择具有给定属性的所有元素。                           |
+-------------------------+--------------------------------------------------------+
| "[@attrib='value']"     | 选择给定属性具有给定值的所有元素。该值不能包含引号。   |
+-------------------------+--------------------------------------------------------+
| "[tag]"                 | 选择所有包含 "tag" 子元素的元素。只支持直系子元素。    |
+-------------------------+--------------------------------------------------------+
| "[.='text']"            | 选择完整文本内容等于 "text" 的所有元素（包括后代）。   |
|                         | 3.7 版新加入.                                          |
+-------------------------+--------------------------------------------------------+
| "[tag='text']"          | 选择所有包含名为 "tag" 的子元素的元素，这些子元素（包  |
|                         | 括后代）的完整文 本内容等于给定的 "text" 。            |
+-------------------------+--------------------------------------------------------+
| "[position]"            | Selects all elements that are located at the given     |
|                         | position.  The position can be either an integer (1 is |
|                         | the first position), the expression "last()" (for the  |
|                         | last position), or a position relative to the last     |
|                         | position (e.g. "last()-1").                            |
+-------------------------+--------------------------------------------------------+

谓词（方括号内的表达式）之前必须带有标签名称，星号或其他谓词。
"position" 谓词前必须有标签名称。


参考引用
========


函数
----

xml.etree.ElementTree.canonicalize(xml_data=None, *, out=None, from_file=None, **options)

   C14N 2.0  转换功能。.

   Canonicalization is a way to normalise XML output in a way that
   allows byte-by-byte comparisons and digital signatures.  It reduced
   the freedom that XML serializers have and instead generates a more
   constrained XML representation.  The main restrictions regard the
   placement of namespace declarations, the ordering of attributes,
   and ignorable whitespace.

   This function takes an XML data string (*xml_data*) or a file path
   or file-like object (*from_file*) as input, converts it to the
   canonical form, and writes it out using the *out* file(-like)
   object, if provided, or returns it as a text string if not.  The
   output file receives text, not bytes.  It should therefore be
   opened in text mode with "utf-8" encoding.

   典型使用:

      xml_data = "<root>...</root>"
      print(canonicalize(xml_data))

      with open("c14n_output.xml", mode='w', encoding='utf-8') as out_file:
          canonicalize(xml_data, out=out_file)

      with open("c14n_output.xml", mode='w', encoding='utf-8') as out_file:
          canonicalize(from_file="inputfile.xml", out=out_file)

   The configuration *options* are as follows:

   * *with_comments*: set to true to include comments (default: false)

   * *strip_text*: set to true to strip whitespace before and after
     text content
        （默认值：否）

   * *rewrite_prefixes*: set to true to replace namespace prefixes by
     "n{number}"
        （默认值：否）

   * *qname_aware_tags*: a set of qname aware tag names in which
     prefixes
        should be replaced in text content (default: empty)

   * *qname_aware_attrs*: a set of qname aware attribute names in
     which prefixes
        should be replaced in text content (default: empty)

   * *exclude_attrs*: a set of attribute names that should not be
     serialised

   * *exclude_tags*: a set of tag names that should not be serialised

   In the option list above, "a set" refers to any collection or
   iterable of strings, no ordering is expected.

   3.8 版新加入.

xml.etree.ElementTree.Comment(text=None)

   Comment element factory.  This factory function creates a special
   element that will be serialized as an XML comment by the standard
   serializer.  The comment string can be either a bytestring or a
   Unicode string.  *text* is a string containing the comment string.
   Returns an element instance representing a comment.

   Note that "XMLParser" skips over comments in the input instead of
   creating comment objects for them. An "ElementTree" will only
   contain comment nodes if they have been inserted into to the tree
   using one of the "Element" methods.

xml.etree.ElementTree.dump(elem)

   Writes an element tree or element structure to sys.stdout.  This
   function should be used for debugging only.

   The exact output format is implementation dependent.  In this
   version, it's written as an ordinary XML file.

   *elem* is an element tree or an individual element.

   3.8 版更變: The "dump()" function now preserves the attribute order
   specified by the user.

xml.etree.ElementTree.fromstring(text, parser=None)

   Parses an XML section from a string constant.  Same as "XML()".
   *text* is a string containing XML data.  *parser* is an optional
   parser instance. If not given, the standard "XMLParser" parser is
   used. Returns an "Element" instance.

xml.etree.ElementTree.fromstringlist(sequence, parser=None)

   Parses an XML document from a sequence of string fragments.
   *sequence* is a list or other sequence containing XML data
   fragments.  *parser* is an optional parser instance.  If not given,
   the standard "XMLParser" parser is used.  Returns an "Element"
   instance.

   3.2 版新加入.

xml.etree.ElementTree.indent(tree, space="  ", level=0)

   Appends whitespace to the subtree to indent the tree visually. This
   can be used to generate pretty-printed XML output. *tree* can be an
   Element or ElementTree.  *space* is the whitespace string that will
   be inserted for each indentation level, two space characters by
   default.  For indenting partial subtrees inside of an already
   indented tree, pass the initial indentation level as *level*.

   3.9 版新加入.

xml.etree.ElementTree.iselement(element)

   Check if an object appears to be a valid element object.  *element*
   is an element instance.  Return "True" if this is an element
   object.

xml.etree.ElementTree.iterparse(source, events=None, parser=None)

   Parses an XML section into an element tree incrementally, and
   reports what's going on to the user.  *source* is a filename or
   *file object* containing XML data.  *events* is a sequence of
   events to report back.  The supported events are the strings
   ""start"", ""end"", ""comment"", ""pi"", ""start-ns"" and ""end-
   ns"" (the "ns" events are used to get detailed namespace
   information).  If *events* is omitted, only ""end"" events are
   reported. *parser* is an optional parser instance.  If not given,
   the standard "XMLParser" parser is used.  *parser* must be a
   subclass of "XMLParser" and can only use the default "TreeBuilder"
   as a target.  Returns an *iterator* providing "(event, elem)"
   pairs.

   Note that while "iterparse()" builds the tree incrementally, it
   issues blocking reads on *source* (or the file it names).  As such,
   it's unsuitable for applications where blocking reads can't be
   made.  For fully non-blocking parsing, see "XMLPullParser".

   備註:

     "iterparse()" only guarantees that it has seen the ">" character
     of a starting tag when it emits a "start" event, so the
     attributes are defined, but the contents of the text and tail
     attributes are undefined at that point.  The same applies to the
     element children; they may or may not be present.If you need a
     fully populated element, look for "end" events instead.

   3.4 版後已棄用: *parser* 参数。

   3.8 版更變: The "comment" and "pi" events were added.

xml.etree.ElementTree.parse(source, parser=None)

   Parses an XML section into an element tree.  *source* is a filename
   or file object containing XML data.  *parser* is an optional parser
   instance.  If not given, the standard "XMLParser" parser is used.
   Returns an "ElementTree" instance.

xml.etree.ElementTree.ProcessingInstruction(target, text=None)

   PI element factory.  This factory function creates a special
   element that will be serialized as an XML processing instruction.
   *target* is a string containing the PI target.  *text* is a string
   containing the PI contents, if given.  Returns an element instance,
   representing a processing instruction.

   Note that "XMLParser" skips over processing instructions in the
   input instead of creating comment objects for them. An
   "ElementTree" will only contain processing instruction nodes if
   they have been inserted into to the tree using one of the "Element"
   methods.

xml.etree.ElementTree.register_namespace(prefix, uri)

   Registers a namespace prefix.  The registry is global, and any
   existing mapping for either the given prefix or the namespace URI
   will be removed. *prefix* is a namespace prefix.  *uri* is a
   namespace uri.  Tags and attributes in this namespace will be
   serialized with the given prefix, if at all possible.

   3.2 版新加入.

xml.etree.ElementTree.SubElement(parent, tag, attrib={}, **extra)

   Subelement factory.  This function creates an element instance, and
   appends it to an existing element.

   The element name, attribute names, and attribute values can be
   either bytestrings or Unicode strings.  *parent* is the parent
   element.  *tag* is the subelement name.  *attrib* is an optional
   dictionary, containing element attributes.  *extra* contains
   additional attributes, given as keyword arguments.  Returns an
   element instance.

xml.etree.ElementTree.tostring(element, encoding="us-ascii", method="xml", *, xml_declaration=None, default_namespace=None, short_empty_elements=True)

   Generates a string representation of an XML element, including all
   subelements.  *element* is an "Element" instance.  *encoding* [1]
   is the output encoding (default is US-ASCII).  Use
   "encoding="unicode"" to generate a Unicode string (otherwise, a
   bytestring is generated).  *method* is either ""xml"", ""html"" or
   ""text"" (default is ""xml""). *xml_declaration*,
   *default_namespace* and *short_empty_elements* has the same meaning
   as in "ElementTree.write()". Returns an (optionally) encoded string
   containing the XML data.

   3.4 版新加入: *short_empty_elements* 形参。

   3.8 版新加入: The *xml_declaration* and *default_namespace*
   parameters.

   3.8 版更變: The "tostring()" function now preserves the attribute
   order specified by the user.

xml.etree.ElementTree.tostringlist(element, encoding="us-ascii", method="xml", *, xml_declaration=None, default_namespace=None, short_empty_elements=True)

   Generates a string representation of an XML element, including all
   subelements.  *element* is an "Element" instance.  *encoding* [1]
   is the output encoding (default is US-ASCII).  Use
   "encoding="unicode"" to generate a Unicode string (otherwise, a
   bytestring is generated).  *method* is either ""xml"", ""html"" or
   ""text"" (default is ""xml""). *xml_declaration*,
   *default_namespace* and *short_empty_elements* has the same meaning
   as in "ElementTree.write()". Returns a list of (optionally) encoded
   strings containing the XML data. It does not guarantee any specific
   sequence, except that "b"".join(tostringlist(element)) ==
   tostring(element)".

   3.2 版新加入.

   3.4 版新加入: *short_empty_elements* 形参。

   3.8 版新加入: The *xml_declaration* and *default_namespace*
   parameters.

   3.8 版更變: The "tostringlist()" function now preserves the
   attribute order specified by the user.

xml.etree.ElementTree.XML(text, parser=None)

   Parses an XML section from a string constant.  This function can be
   used to embed "XML literals" in Python code.  *text* is a string
   containing XML data.  *parser* is an optional parser instance.  If
   not given, the standard "XMLParser" parser is used.  Returns an
   "Element" instance.

xml.etree.ElementTree.XMLID(text, parser=None)

   Parses an XML section from a string constant, and also returns a
   dictionary which maps from element id:s to elements.  *text* is a
   string containing XML data.  *parser* is an optional parser
   instance.  If not given, the standard "XMLParser" parser is used.
   Returns a tuple containing an "Element" instance and a dictionary.


XInclude 支持
=============

This module provides limited support for XInclude directives, via the
"xml.etree.ElementInclude" helper module.  This module can be used to
insert subtrees and text strings into element trees, based on
information in the tree.


示例
----

Here's an example that demonstrates use of the XInclude module. To
include an XML document in the current document, use the
"{http://www.w3.org/2001/XInclude}include" element and set the
**parse** attribute to ""xml"", and use the **href** attribute to
specify the document to include.

   <?xml version="1.0"?>
   <document xmlns:xi="http://www.w3.org/2001/XInclude">
     <xi:include href="source.xml" parse="xml" />
   </document>

By default, the **href** attribute is treated as a file name. You can
use custom loaders to override this behaviour. Also note that the
standard helper does not support XPointer syntax.

To process this file, load it as usual, and pass the root element to
the "xml.etree.ElementTree" module:

   from xml.etree import ElementTree, ElementInclude

   tree = ElementTree.parse("document.xml")
   root = tree.getroot()

   ElementInclude.include(root)

The ElementInclude module replaces the
"{http://www.w3.org/2001/XInclude}include" element with the root
element from the **source.xml** document. The result might look
something like this:

   <document xmlns:xi="http://www.w3.org/2001/XInclude">
     <para>This is a paragraph.</para>
   </document>

If the **parse** attribute is omitted, it defaults to "xml". The href
attribute is required.

To include a text document, use the
"{http://www.w3.org/2001/XInclude}include" element, and set the
**parse** attribute to "text":

   <?xml version="1.0"?>
   <document xmlns:xi="http://www.w3.org/2001/XInclude">
     Copyright (c) <xi:include href="year.txt" parse="text" />.
   </document>

结果可能如下所示：

   <document xmlns:xi="http://www.w3.org/2001/XInclude">
     Copyright (c) 2003.
   </document>


参考引用
========


函数
----

xml.etree.ElementInclude.default_loader(href, parse, encoding=None)

   Default loader. This default loader reads an included resource from
   disk.  *href* is a URL. *parse* is for parse mode either "xml" or
   "text".  *encoding* is an optional text encoding.  If not given,
   encoding is "utf-8".  Returns the expanded resource.  If the parse
   mode is ""xml"", this is an ElementTree instance.  If the parse
   mode is "text", this is a Unicode string.  If the loader fails, it
   can return None or raise an exception.

xml.etree.ElementInclude.include(elem, loader=None, base_url=None, max_depth=6)

   This function expands XInclude directives.  *elem* is the root
   element.  *loader* is an optional resource loader.  If omitted, it
   defaults to "default_loader()". If given, it should be a callable
   that implements the same interface as "default_loader()".
   *base_url* is base URL of the original file, to resolve relative
   include file references.  *max_depth* is the maximum number of
   recursive inclusions.  Limited to reduce the risk of malicious
   content explosion. Pass a negative value to disable the limitation.

   Returns the expanded resource.  If the parse mode is ""xml"", this
   is an ElementTree instance.  If the parse mode is "text", this is a
   Unicode string.  If the loader fails, it can return None or raise
   an exception.

   3.9 版新加入: The *base_url* and *max_depth* parameters.


元素对象
--------

class xml.etree.ElementTree.Element(tag, attrib={}, **extra)

   Element class.  This class defines the Element interface, and
   provides a reference implementation of this interface.

   The element name, attribute names, and attribute values can be
   either bytestrings or Unicode strings.  *tag* is the element name.
   *attrib* is an optional dictionary, containing element attributes.
   *extra* contains additional attributes, given as keyword arguments.

   tag

      一个标识此元素意味着何种数据的字符串(换句话说，元素类型)。

   text
   tail

      These attributes can be used to hold additional data associated
      with the element.  Their values are usually strings but may be
      any application-specific object.  If the element is created from
      an XML file, the *text* attribute holds either the text between
      the element's start tag and its first child or end tag, or
      "None", and the *tail* attribute holds either the text between
      the element's end tag and the next tag, or "None".  For the XML
      data

         <a><b>1<c>2<d/>3</c></b>4</a>

      the *a* element has "None" for both *text* and *tail*
      attributes, the *b* element has *text* ""1"" and *tail* ""4"",
      the *c* element has *text* ""2"" and *tail* "None", and the *d*
      element has *text* "None" and *tail* ""3"".

      To collect the inner text of an element, see "itertext()", for
      example """.join(element.itertext())".

      Applications may store arbitrary objects in these attributes.

   attrib

      A dictionary containing the element's attributes.  Note that
      while the *attrib* value is always a real mutable Python
      dictionary, an ElementTree implementation may choose to use
      another internal representation, and create the dictionary only
      if someone asks for it.  To take advantage of such
      implementations, use the dictionary methods below whenever
      possible.

   The following dictionary-like methods work on the element
   attributes.

   clear()

      Resets an element.  This function removes all subelements,
      clears all attributes, and sets the text and tail attributes to
      "None".

   get(key, default=None)

      Gets the element attribute named *key*.

      Returns the attribute value, or *default* if the attribute was
      not found.

   items()

      Returns the element attributes as a sequence of (name, value)
      pairs.  The attributes are returned in an arbitrary order.

   keys()

      Returns the elements attribute names as a list.  The names are
      returned in an arbitrary order.

   set(key, value)

      Set the attribute *key* on the element to *value*.

   The following methods work on the element's children (subelements).

   append(subelement)

      Adds the element *subelement* to the end of this element's
      internal list of subelements.  Raises "TypeError" if
      *subelement* is not an "Element".

   extend(subelements)

      Appends *subelements* from a sequence object with zero or more
      elements. Raises "TypeError" if a subelement is not an
      "Element".

      3.2 版新加入.

   find(match, namespaces=None)

      Finds the first subelement matching *match*.  *match* may be a
      tag name or a path.  Returns an element instance or "None".
      *namespaces* is an optional mapping from namespace prefix to
      full name.  Pass "''" as prefix to move all unprefixed tag names
      in the expression into the given namespace.

   findall(match, namespaces=None)

      Finds all matching subelements, by tag name or path.  Returns a
      list containing all matching elements in document order.
      *namespaces* is an optional mapping from namespace prefix to
      full name.  Pass "''" as prefix to move all unprefixed tag names
      in the expression into the given namespace.

   findtext(match, default=None, namespaces=None)

      Finds text for the first subelement matching *match*.  *match*
      may be a tag name or a path.  Returns the text content of the
      first matching element, or *default* if no element was found.
      Note that if the matching element has no text content an empty
      string is returned. *namespaces* is an optional mapping from
      namespace prefix to full name.  Pass "''" as prefix to move all
      unprefixed tag names in the expression into the given namespace.

   insert(index, subelement)

      Inserts *subelement* at the given position in this element.
      Raises "TypeError" if *subelement* is not an "Element".

   iter(tag=None)

      Creates a tree *iterator* with the current element as the root.
      The iterator iterates over this element and all elements below
      it, in document (depth first) order.  If *tag* is not "None" or
      "'*'", only elements whose tag equals *tag* are returned from
      the iterator.  If the tree structure is modified during
      iteration, the result is undefined.

      3.2 版新加入.

   iterfind(match, namespaces=None)

      Finds all matching subelements, by tag name or path.  Returns an
      iterable yielding all matching elements in document order.
      *namespaces* is an optional mapping from namespace prefix to
      full name.

      3.2 版新加入.

   itertext()

      Creates a text iterator.  The iterator loops over this element
      and all subelements, in document order, and returns all inner
      text.

      3.2 版新加入.

   makeelement(tag, attrib)

      Creates a new element object of the same type as this element.
      Do not call this method, use the "SubElement()" factory function
      instead.

   remove(subelement)

      Removes *subelement* from the element.  Unlike the find* methods
      this method compares elements based on the instance identity,
      not on tag value or contents.

   "Element" objects also support the following sequence type methods
   for working with subelements: "__delitem__()", "__getitem__()",
   "__setitem__()", "__len__()".

   Caution: Elements with no subelements will test as "False".  This
   behavior will change in future versions.  Use specific "len(elem)"
   or "elem is None" test instead.

      element = root.find('foo')

      if not element:  # careful!
          print("element not found, or element has no subelements")

      if element is None:
          print("element not found")

   Prior to Python 3.8, the serialisation order of the XML attributes
   of elements was artificially made predictable by sorting the
   attributes by their name. Based on the now guaranteed ordering of
   dicts, this arbitrary reordering was removed in Python 3.8 to
   preserve the order in which attributes were originally parsed or
   created by user code.

   In general, user code should try not to depend on a specific
   ordering of attributes, given that the XML Information Set
   explicitly excludes the attribute order from conveying information.
   Code should be prepared to deal with any ordering on input. In
   cases where deterministic XML output is required, e.g. for
   cryptographic signing or test data sets, canonical serialisation is
   available with the "canonicalize()" function.

   In cases where canonical output is not applicable but a specific
   attribute order is still desirable on output, code should aim for
   creating the attributes directly in the desired order, to avoid
   perceptual mismatches for readers of the code. In cases where this
   is difficult to achieve, a recipe like the following can be applied
   prior to serialisation to enforce an order independently from the
   Element creation:

      def reorder_attributes(root):
          for el in root.iter():
              attrib = el.attrib
              if len(attrib) > 1:
                  # adjust attribute order, e.g. by sorting
                  attribs = sorted(attrib.items())
                  attrib.clear()
                  attrib.update(attribs)


ElementTree 对象
----------------

class xml.etree.ElementTree.ElementTree(element=None, file=None)

   ElementTree wrapper class.  This class represents an entire element
   hierarchy, and adds some extra support for serialization to and
   from standard XML.

   *element* is the root element.  The tree is initialized with the
   contents of the XML *file* if given.

   _setroot(element)

      Replaces the root element for this tree.  This discards the
      current contents of the tree, and replaces it with the given
      element.  Use with care.  *element* is an element instance.

   find(match, namespaces=None)

      Same as "Element.find()", starting at the root of the tree.

   findall(match, namespaces=None)

      Same as "Element.findall()", starting at the root of the tree.

   findtext(match, default=None, namespaces=None)

      Same as "Element.findtext()", starting at the root of the tree.

   getroot()

      Returns the root element for this tree.

   iter(tag=None)

      Creates and returns a tree iterator for the root element.  The
      iterator loops over all elements in this tree, in section order.
      *tag* is the tag to look for (default is to return all
      elements).

   iterfind(match, namespaces=None)

      Same as "Element.iterfind()", starting at the root of the tree.

      3.2 版新加入.

   parse(source, parser=None)

      Loads an external XML section into this element tree.  *source*
      is a file name or *file object*.  *parser* is an optional parser
      instance. If not given, the standard "XMLParser" parser is used.
      Returns the section root element.

   write(file, encoding="us-ascii", xml_declaration=None, default_namespace=None, method="xml", *, short_empty_elements=True)

      Writes the element tree to a file, as XML.  *file* is a file
      name, or a *file object* opened for writing.  *encoding* [1] is
      the output encoding (default is US-ASCII). *xml_declaration*
      controls if an XML declaration should be added to the file.  Use
      "False" for never, "True" for always, "None" for only if not US-
      ASCII or UTF-8 or Unicode (default is "None").
      *default_namespace* sets the default XML namespace (for
      "xmlns"). *method* is either ""xml"", ""html"" or ""text""
      (default is ""xml""). The keyword-only *short_empty_elements*
      parameter controls the formatting of elements that contain no
      content.  If "True" (the default), they are emitted as a single
      self-closed tag, otherwise they are emitted as a pair of
      start/end tags.

      The output is either a string ("str") or binary ("bytes"). This
      is controlled by the *encoding* argument.  If *encoding* is
      ""unicode"", the output is a string; otherwise, it's binary.
      Note that this may conflict with the type of *file* if it's an
      open *file object*; make sure you do not try to write a string
      to a binary stream and vice versa.

      3.4 版新加入: *short_empty_elements* 形参。

      3.8 版更變: The "write()" method now preserves the attribute
      order specified by the user.

This is the XML file that is going to be manipulated:

   <html>
       <head>
           <title>Example page</title>
       </head>
       <body>
           <p>Moved to <a href="http://example.org/">example.org</a>
           or <a href="http://example.com/">example.com</a>.</p>
       </body>
   </html>

Example of changing the attribute "target" of every link in first
paragraph:

   >>> from xml.etree.ElementTree import ElementTree
   >>> tree = ElementTree()
   >>> tree.parse("index.xhtml")
   <Element 'html' at 0xb77e6fac>
   >>> p = tree.find("body/p")     # Finds first occurrence of tag p in body
   >>> p
   <Element 'p' at 0xb77ec26c>
   >>> links = list(p.iter("a"))   # Returns list of all links
   >>> links
   [<Element 'a' at 0xb77ec2ac>, <Element 'a' at 0xb77ec1cc>]
   >>> for i in links:             # Iterates through all found links
   ...     i.attrib["target"] = "blank"
   >>> tree.write("output.xhtml")


QName Objects
-------------

class xml.etree.ElementTree.QName(text_or_uri, tag=None)

   QName wrapper.  This can be used to wrap a QName attribute value,
   in order to get proper namespace handling on output.  *text_or_uri*
   is a string containing the QName value, in the form {uri}local, or,
   if the tag argument is given, the URI part of a QName.  If *tag* is
   given, the first argument is interpreted as a URI, and this
   argument is interpreted as a local name. "QName" instances are
   opaque.


TreeBuilder Objects
-------------------

class xml.etree.ElementTree.TreeBuilder(element_factory=None, *, comment_factory=None, pi_factory=None, insert_comments=False, insert_pis=False)

   Generic element structure builder.  This builder converts a
   sequence of start, data, end, comment and pi method calls to a
   well-formed element structure.  You can use this class to build an
   element structure using a custom XML parser, or a parser for some
   other XML-like format.

   *element_factory*, when given, must be a callable accepting two
   positional arguments: a tag and a dict of attributes.  It is
   expected to return a new element instance.

   The *comment_factory* and *pi_factory* functions, when given,
   should behave like the "Comment()" and "ProcessingInstruction()"
   functions to create comments and processing instructions.  When not
   given, the default factories will be used.  When *insert_comments*
   and/or *insert_pis* is true, comments/pis will be inserted into the
   tree if they appear within the root element (but not outside of
   it).

   close()

      Flushes the builder buffers, and returns the toplevel document
      element.  Returns an "Element" instance.

   data(data)

      Adds text to the current element.  *data* is a string.  This
      should be either a bytestring, or a Unicode string.

   end(tag)

      Closes the current element.  *tag* is the element name.  Returns
      the closed element.

   start(tag, attrs)

      Opens a new element.  *tag* is the element name.  *attrs* is a
      dictionary containing element attributes.  Returns the opened
      element.

   comment(text)

      Creates a comment with the given *text*.  If "insert_comments"
      is true, this will also add it to the tree.

      3.8 版新加入.

   pi(target, text)

      Creates a comment with the given *target* name and *text*.  If
      "insert_pis" is true, this will also add it to the tree.

      3.8 版新加入.

   In addition, a custom "TreeBuilder" object can provide the
   following methods:

   doctype(name, pubid, system)

      Handles a doctype declaration.  *name* is the doctype name.
      *pubid* is the public identifier.  *system* is the system
      identifier.  This method does not exist on the default
      "TreeBuilder" class.

      3.2 版新加入.

   start_ns(prefix, uri)

      Is called whenever the parser encounters a new namespace
      declaration, before the "start()" callback for the opening
      element that defines it. *prefix* is "''" for the default
      namespace and the declared namespace prefix name otherwise.
      *uri* is the namespace URI.

      3.8 版新加入.

   end_ns(prefix)

      Is called after the "end()" callback of an element that declared
      a namespace prefix mapping, with the name of the *prefix* that
      went out of scope.

      3.8 版新加入.

class xml.etree.ElementTree.C14NWriterTarget(write, *, with_comments=False, strip_text=False, rewrite_prefixes=False, qname_aware_tags=None, qname_aware_attrs=None, exclude_attrs=None, exclude_tags=None)

   A C14N 2.0 writer.  Arguments are the same as for the
   "canonicalize()" function.  This class does not build a tree but
   translates the callback events directly into a serialised form
   using the *write* function.

   3.8 版新加入.


XMLParser对象
-------------

class xml.etree.ElementTree.XMLParser(*, target=None, encoding=None)

   This class is the low-level building block of the module.  It uses
   "xml.parsers.expat" for efficient, event-based parsing of XML.  It
   can be fed XML data incrementally with the "feed()" method, and
   parsing events are translated to a push API - by invoking callbacks
   on the *target* object.  If *target* is omitted, the standard
   "TreeBuilder" is used. If *encoding* [1] is given, the value
   overrides the encoding specified in the XML file.

   3.8 版更變: Parameters are now keyword-only. The *html* argument no
   longer supported.

   close()

      Finishes feeding data to the parser.  Returns the result of
      calling the "close()" method of the *target* passed during
      construction; by default, this is the toplevel document element.

   feed(data)

      Feeds data to the parser.  *data* is encoded data.

   "XMLParser.feed()" calls *target*'s "start(tag, attrs_dict)" method
   for each opening tag, its "end(tag)" method for each closing tag,
   and data is processed by method "data(data)".  For further
   supported callback methods, see the "TreeBuilder" class.
   "XMLParser.close()" calls *target*'s method "close()". "XMLParser"
   can be used not only for building a tree structure. This is an
   example of counting the maximum depth of an XML file:

      >>> from xml.etree.ElementTree import XMLParser
      >>> class MaxDepth:                     # The target object of the parser
      ...     maxDepth = 0
      ...     depth = 0
      ...     def start(self, tag, attrib):   # Called for each opening tag.
      ...         self.depth += 1
      ...         if self.depth > self.maxDepth:
      ...             self.maxDepth = self.depth
      ...     def end(self, tag):             # Called for each closing tag.
      ...         self.depth -= 1
      ...     def data(self, data):
      ...         pass            # We do not need to do anything with data.
      ...     def close(self):    # Called when all data has been parsed.
      ...         return self.maxDepth
      ...
      >>> target = MaxDepth()
      >>> parser = XMLParser(target=target)
      >>> exampleXml = """
      ... <a>
      ...   <b>
      ...   </b>
      ...   <b>
      ...     <c>
      ...       <d>
      ...       </d>
      ...     </c>
      ...   </b>
      ... </a>"""
      >>> parser.feed(exampleXml)
      >>> parser.close()
      4


XMLPullParser对象
-----------------

class xml.etree.ElementTree.XMLPullParser(events=None)

   A pull parser suitable for non-blocking applications.  Its input-
   side API is similar to that of "XMLParser", but instead of pushing
   calls to a callback target, "XMLPullParser" collects an internal
   list of parsing events and lets the user read from it. *events* is
   a sequence of events to report back.  The supported events are the
   strings ""start"", ""end"", ""comment"", ""pi"", ""start-ns"" and
   ""end-ns"" (the "ns" events are used to get detailed namespace
   information).  If *events* is omitted, only ""end"" events are
   reported.

   feed(data)

      Feed the given bytes data to the parser.

   close()

      Signal the parser that the data stream is terminated. Unlike
      "XMLParser.close()", this method always returns "None". Any
      events not yet retrieved when the parser is closed can still be
      read with "read_events()".

   read_events()

      Return an iterator over the events which have been encountered
      in the data fed to the parser.  The iterator yields "(event,
      elem)" pairs, where *event* is a string representing the type of
      event (e.g. ""end"") and *elem* is the encountered "Element"
      object, or other context value as follows.

      * "start", "end": the current Element.

      * "comment", "pi": the current comment / processing instruction

      * "start-ns": a tuple "(prefix, uri)" naming the declared
        namespace mapping.

      * "end-ns": "None" (this may change in a future version)

      Events provided in a previous call to "read_events()" will not
      be yielded again.  Events are consumed from the internal queue
      only when they are retrieved from the iterator, so multiple
      readers iterating in parallel over iterators obtained from
      "read_events()" will have unpredictable results.

   備註:

     "XMLPullParser" only guarantees that it has seen the ">"
     character of a starting tag when it emits a "start" event, so the
     attributes are defined, but the contents of the text and tail
     attributes are undefined at that point.  The same applies to the
     element children; they may or may not be present.If you need a
     fully populated element, look for "end" events instead.

   3.4 版新加入.

   3.8 版更變: The "comment" and "pi" events were added.


异常
----

class xml.etree.ElementTree.ParseError

   XML parse error, raised by the various parsing methods in this
   module when parsing fails.  The string representation of an
   instance of this exception will contain a user-friendly error
   message.  In addition, it will have the following attributes
   available:

   code

      A numeric error code from the expat parser. See the
      documentation of "xml.parsers.expat" for the list of error codes
      and their meanings.

   position

      A tuple of *line*, *column* numbers, specifying where the error
      occurred.

-[ 註解 ]-

[1] The encoding string included in XML output should conform to the
    appropriate standards.  For example, "UTF-8" is valid, but "UTF8"
    is not.  See https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-
    EncodingDecl and https://www.iana.org/assignments/character-sets
    /character-sets.xhtml.
