# `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: 此模块将在可能的情况下使用快速实现。

3.3 版後已棄用: `xml.etree.cElementTree` 模块已被弃用。

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 是一种继承性的分层数据格式，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` 构造器来访问文档类型声明。

### 用于非阻塞解析的拉取 API

此模块所提供了大多数解析函数都要求在返回任何结果之前一次性读取整个文档。 可以使用 `XMLParser` 并以增量方式添加数据，但这是在回调目标上调用方法的推送式 API。 有时用户真正想要的是能够以增量方式解析 XML 而无需阻塞操作，同时享受完整的已构造 `Element` 对象。

针对此需求的最强大工具是 `XMLPullParser`。 它不要求通过阻塞式读取来获得 XML 数据，而是通过执行 `XMLPullParser.feed()` 调用来增量式地添加数据。 要获得已解析的 XML 元素，应调用 `XMLPullParser.read_events()`。 下面是一个示例:

    >>> 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

常见的用例是针对以非阻塞方式进行的应用程序，其中 XML 是从套接字接收或从某些存储设备增量式读取的。 在这些用例中，阻塞式读取是不可接受的。

因为其非常灵活，`XMLPullParser` 在更简单的用例中使用起来可能并不方便。 如果你不介意你的应用程序在读取 XML 数据时造成阻塞但仍希望具有增量解析能力，可以考虑 `iterparse()`。 它在你读取大型 XML 文档并且不希望将它完全放去内存时会很适用。

### 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')

请注意在迭代时进行并发修改可能会导致问题，就像在迭代并修改 Python 列表或字典时那样。 因此，这个示例先通过 `root.findall()` 收集了所有匹配的元素，在此之后再对匹配项列表进行迭代。

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>

### 解析带有命名空间的 XML

如果 XML 输入带有 命名空间，则具有前缀的 `prefix:sometag` 形式的标记和属性将被扩展为 `{uri}sometag`，其中 prefix 会被完整 URI 所替换。 并且，如果存在 默认命名空间，则完整 URI 会被添加到所有未加前缀的标记之前。

下面的 XML 示例包含两个命名空间，一个具有前缀 "fictional" 而另一个则作为默认命名空间:

    <?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>

搜索和探查这个 XML 示例的一种方式是手动为 `find()` 或 `findall()` 的 xpath 中的每个标记或属性添加 URI:

    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)

一种更好的方式是搜索带命名空间的 XML 示例创建一个字典来存放你自己的前缀并在搜索函数中使用它们:

    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)

这两种方式都会输出:

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

### 其他资源

请访问 http://effbot.org/zone/element-index.htm 获取教程和其他文档的链接。

## XPath支持

此模块提供了对 XPath 表达式 的有限支持用于在树中定位元素。 其目标是支持一个简化语法的较小子集；完整的 XPath 引擎超出了此模块的适用范围。

### 示例

下面是一个演示此模块的部分 XPath 功能的例子。 我们将使用来自 解析 XML 小节的 `countrydata` XML 文档:

    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]")

对于带有命名空间的 XML，应使用通常的限定 `{namespace}tag` 标记法:

    # 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` | 选择具有给定标记的所有子元素。 例如，`spam` 是选择名为 `spam` 的所有子元素，而 `spam/egg` 是在名为 `spam` 的子元素中选择所有名为 `egg` 的孙元素，`{*}spam` 是在任意（或无）命名空间中选择名为 `spam` 的标记，而 `{}*` 是只选择不在一个命名空间中的标记。 3.8 版更變: 增加了对星号通配符的支持。
`*` | 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。
`//` | 选择所有子元素 在当前元素的所有下级中选择所有下级元素。 例如，`.//egg` 是在整个树中选择所有 `egg` 元素。
`..` | 选择父元素。 如果路径试图前往起始元素的上级（元素的 `find` 被调用）则返回 `None`。
`[@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]` | 选择位于给定位置的所有元素。 位置可以是一个整数 (1 表示首位)，表达式 `last()` (表示末位)，或者相对于末位的位置 (例如 `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。.

  规整化是标准化 XML 输出的一种方式，该方式允许按字节比较和数字签名。 它降低了 XML 序列化器所具有的自由度并改为生成更受约束的 XML 表示形式。 主要限制涉及命名空间声明的位置、属性的顺序和可忽略的空白符等。

  此函数接受一个 XML 数字字符串 (xml_data) 或文件路径或者文件类对象 (from_file) 作为输入，将其转换为规整形式，并在提供了 out 文件（类）对象的情况下将其写到该对象的话，或者如果未提供则将其作为文本字符串返回。 输出文件接受文本而非字节数据。 因此它应当以使用 `utf-8` 编码格式的文本模式来打开。

  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)

  配置选项 options 如下:

  - with_comments: 设为真值以包括注释 (默认为假值)

  - strip_text: 设为真值以去除文本内容前后的空白符

      （默认值：否）

  - rewrite_prefixes: 设为真值以替换带有 "n{number}" 前缀的命名空间

      （默认值：否）

  - qname_aware_tags: 一组可感知限定名称的标记名称，其中的前缀

      应当在文本内容中被替换 (默认为空值)

  - qname_aware_attrs: 一组可感知限定名称的属性名称，其中的前缀

      应当在文本内容中被替换 (默认为空值)

  - exclude_attrs: 一组不应当被序列化的属性名称

  - exclude_tags: 一组不应当被序列化的标记名称

  在上面的选项列表中，"一组" 是指任意多项集或包含字符串的可迭代对象，排序是不必要的。

  3.8 版新加入.

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

  注释元素工厂函数。 这个工厂函数可创建一个特殊元素，它将被标准序列化器当作 XML 注释来进行序列化。 注释字串可以是字节串或是 Unicode 字符串。 text 是包含注释字串的字符串。 返回一个表示注释的元素实例。

  请注意 `XMLParser` 会跳过输入中的注释而不会为其创建注释对象。 `ElementTree` 将只在当使用某个 `Element` 方法向树插入了注释节点时才会包含注释节点。

`xml.etree.ElementTree.``dump`(elem)

  将一个元素树或元素结构体写入到 sys.stdout。 此函数应当只被用于调试。

  实际输出格式是依赖于具体实现的。 在这个版本中，它将以普通 XML 文件的格式写入。

  elem 是一个元素树或单独元素。

  3.8 版更變: `dump()` 函数现在会保留用户指定的属性顺序。

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

  根据一个字符串常量解析 XML 的节。 与 `XML()` 类似。 text 是包含 XML 数据的字符串。 parser 是可选的解析器实例。 如果未给出，则会使用标准 `XMLParser` 解析器。 返回一个 `Element` 实例。

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

  根据一个字符串片段序列解析 XML 文档。 sequence 是包含 XML 数据片段的列表或其他序列对象。 parser 是可选的解析器实例。 如果未给出，则会使用标准的 `XMLParser` 解析器。 返回一个 `Element` 实例。

  3.2 版新加入.

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

  添加空格到子树来实现树的缩进效果。 这可以被用来生成美化打印的 XML 输出。 tree 可以为 Element 或 ElementTree。 space 是对应将被插入的每个缩进层级的空格字符串，默认为两个空格符。 要对已缩进的树的部分子树进行缩进，请传入初始缩进层级作为 level。

  3.9 版新加入.

`xml.etree.ElementTree.``iselement`(element)

  检测一个对象是否为有效的元素对象。 element 是一个元素实例。 如果对象是一个元素对象则返回 `True`。

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

  以增量方式将一个 XML 节解析为元素树，并向用户报告执行情况。 source 是包含 XML 数据的文件名或 file object。 events 是要报告的事件序列。 所支持的事件字符串有 `"start"`, `"end"`, `"comment"`, `"pi"`, `"start-ns"` 和 `"end-ns"` ("ns" 事件用于获取详细的命名空间信息)。 如果 events 被省略，则只有 `"end"` 事件会被报告。 parser 是可选的解析器实例。 如果未给出，则会使用标准的 `XMLParser` 解析器。 parser 必须为 `XMLParser` 的子类并且只能使用默认的 `TreeBuilder` 作为目标。 返回一个提供 `(event, elem)` 对的 iterator。

  请注意虽然 `iterparse()` 是以增量方式构建树，但它会对 source (或其所指定的文件) 发出阻塞式读取。 因此，它不适用于不可执行阻塞式读取的应用。 对于完全非阻塞式的解析，请参看 `XMLPullParser`。

  備註

  `iterparse()` 只会确保当发出 "start" 事件时看到了开始标记的 ">" 字符，因而在这个点上属性已被定义，但文本容和末尾属性还未被定义。 这同样适用于元素的下级；它们可能存在也可能不存在。

  如果你需要已完全填充的元素，请改为查找 "end" 事件。

  3.4 版後已棄用: parser 参数。

  3.8 版更變: 增加了 `comment` 和 `pi` 事件。

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

  将一个 XML 的节解析为元素树。 source 是包含 XML 数据的文件名或文件对象。 parser 是可选的解析器实例。 如果未给出，则会使用标准的 `XMLParser` 解析器。 返回一个 `ElementTree` 实例。

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

  PI 元素工厂函数。 这个工厂函数可创建一个特殊元素，它将被当作 XML 处理指令来进行序列化。 target 是包含 PI 目标的字符串。 text 如果给出则是包含 PI 内容的字符串。 返回一个表示处理指令的元素实例。

  请注意 `XMLParser` 会跳过输入中的处理指令而不会为其创建注释对象。 `ElementTree` 将只在当使用某个 `Element` 方法向树插入了处理指令节点时才会包含处理指令节点。

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

  注册一个命名空间前缀。 这个注册表是全局的，并且任何对应给定前缀或命名空间 URI 的现有映射都会被移除。 prefix 是命名空间前缀。 uri 是命名空间 URI。 如果可能的话，这个命名空间中的标记和属性将附带给定的前缀来进行序列化。

  3.2 版新加入.

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

  子元素工厂函数。 这个函数会创建一个元素实例，并将其添加到现有的元素。

  元素名、属性名和属性值可以是字节串或 Unicode 字符串。 parent 是父元素。 tag 是子元素名。 attrib 是一个可选的字典，其中包含元素属性。 extra 包含额外的属性，以关键字参数形式给出。 返回一个元素实例。

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

  生成一个 XML 元素的字符串表示形式，包括所有子元素。 element 是一个 `Element` 实例。 encoding 1 是输出编码格式（默认为 US-ASCII）。 请使用 `encoding="unicode"` 来生成 Unicode 字符串（否则生成字节串）。 method 是 `"xml"`, `"html"` 或 `"text"` (默认为 `"xml"`)。 xml_declaration, default_namespace 和 short_empty_elements 具有与 `ElementTree.write()` 中一致的含义。 返回一个包含 XML 数据（可选）已编码的字符串。

  3.4 版新加入: short_empty_elements 形参。

  3.8 版新加入: xml_declaration 和 default_namespace 形参。

  3.8 版更變: `tostring()` 函数现在会保留用户指定的属性顺序。

`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: xml_declaration 和 default_namespace 形参。

  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.

  如果你需要已完全填充的元素，请改为查找 "end" 事件。

  3.4 版新加入.

  3.8 版更變: 增加了 `comment` 和 `pi` 事件。

### 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(1,2,3,4)

  包括在 XML 输出中的编码格式字符串应当符合适当的标准。 例如 "UTF-8" 是有效的，但 "UTF8" 是无效的。 请参阅 https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl 和 https://www.iana.org/assignments/character-sets/character-sets.xhtml。