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。

在 3.3 版更改: 只要有可能,这个模块将使用快速实现。xml.etree.cElementTree 模块已弃用。

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 Elementroot 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'

注解

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

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 并以渐进方式添加数据,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渐进方式解析 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() 调用来渐进式地添加数据。 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渐进式读取的。 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>

使用命名空间解析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()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。

在 3.8 版更改: 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 新版功能.

[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

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 新版功能.

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。

在 3.8 版更改: 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。 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 新版功能.

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 objectevents 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""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

注解

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 版后已移除: parser 参数。

在 3.8 版更改: 增加了 commentpi 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 新版功能.

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"xml", "html""text" (默认为 "xml")。 xml_declaration, default_namespaceshort_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 新版功能: short_empty_elements 形参。

3.8 新版功能: xml_declarationdefault_namespace 形参。

在 3.8 版更改: 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)

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"xml", "html""text" (默认为 "xml")。 xml_declaration, default_namespaceshort_empty_elements 具有与 ElementTree.write() 中一致的含义。 返回一个包含 XML 数据(可选)已编码字符串的列表。 它并不保证任何特定的序列,除了 b"".join(tostringlist(element)) == tostring(element)

3.2 新版功能.

3.4 新版功能: short_empty_elements 形参。

3.8 新版功能: xml_declarationdefault_namespace 形参。

在 3.8 版更改: tostringlist() 函数现在会保留用户指定的属性顺序。

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

根据一个字符串常量解析 XML 的节。 此函数可被用于在 Python 代码中嵌入“XML 字面值”。 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,则会使用标准的 XMLParser 解析器。 返回一个 Element 实例。

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

根据一个字符串常量解析 XML 的节,并且还将返回一个将元素的 id:s 映射到元素的字典。 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,则会使用标准的 XMLParser 解析器。 返回一个包含 Element 实例和字典的元组。

XInclude 支持

此模块通过 xml.etree.ElementInclude 辅助模块提供了对 XInclude 指令 的有限支持,这个模块可被用来根据元素树的信息在其中插入子树和文本字符串。

示例

以下是一个演示 XInclude 模块用法的例子。 要在当前文本中包括一个 XML 文档,请使用 {http://www.w3.org/2001/XInclude}include 元素并将 parse 属性设为 "xml",并使用 href 属性来指定要包括的文档。

<?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

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)

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(). 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.

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 新版功能.

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.

getchildren()

Deprecated since version 3.2, will be removed in version 3.9: Use list(elem) or iteration.

getiterator(tag=None)

Deprecated since version 3.2, will be removed in version 3.9: Use method Element.iter() instead.

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 新版功能.

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 新版功能.

itertext()

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

3.2 新版功能.

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.

getiterator(tag=None)

Deprecated since version 3.2, will be removed in version 3.9: Use method ElementTree.iter() instead.

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 新版功能.

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 新版功能: short_empty_elements 形参。

在 3.8 版更改: 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 新版功能.

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 新版功能.

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 新版功能.

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 新版功能.

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 新版功能.

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 新版功能.

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.

在 3.8 版更改: 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.

注解

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 新版功能.

在 3.8 版更改: 增加了 commentpi 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.

备注

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-EncodingDeclhttps://www.iana.org/assignments/character-sets/character-sets.xhtml