# 20.5. `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 。

## 20.5.1. 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。

### 20.5.1.1. 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。

### 20.5.1.2. 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>

我们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：

    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` 。确切的信息请检查文档。

作为一个 `Element` ， `root` 有一个标记和一个属性字典:

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

它还有我们可以迭代的子节点：

    >>> 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。

### 20.5.1.3. 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.

### 20.5.1.4. 寻找有趣的元素

`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.text` 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。

### 20.5.1.5. 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。 `ElementTree.write()` 方法可达到此目的。

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。

假设我们要在每个国家/地区的中添加一个排名，并在rank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'):
    ...     rank = int(country.find('rank').text)
    ...     if rank > 50:
    ...         root.remove(country)
    ...
    >>> 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>
    </data>

### 20.5.1.6. 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>

### 20.5.1.7. 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

### 20.5.1.8. 其他资源

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

## 20.5.2. 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.

### 20.5.2.1. 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]")

### 20.5.2.2. 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`.
`*` | Selects all child elements. For example, `*/egg` selects all grandchildren named `egg`.
`.` | 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。
`[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。

## 20.5.3. 参考

### 20.5.3.1. 函数

`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.

`xml.etree.ElementTree.``fromstring`(text)

  Parses an XML section from a string constant. Same as `XML()`. text is a string containing XML data. 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 新版功能.

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

  Checks if an object appears to be a valid element object. element is an element instance. Returns a true value 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"`, `"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`.

  注解

  `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 版后已移除: parser 参数。

`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 新版功能.

`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", *, 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"`). short_empty_elements has the same meaning as in `ElementTree.write()`. Returns an (optionally) encoded string containing the XML data.

  3.4 新版功能: short_empty_elements 形参。

`xml.etree.ElementTree.``tostringlist`(element, encoding="us-ascii", method="xml", *, 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"`). 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 新版功能.

  3.4 新版功能: short_empty_elements 形参。

`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.

### 20.5.3.2. 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.

  `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.

  `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.

  `getchildren`()

    3.2 版后已移除: Use `list(elem)` or iteration.

  `getiterator`(tag=None)

    3.2 版后已移除: 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")

### 20.5.3.3. 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)

    3.2 版后已移除: 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。

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")

### 20.5.3.4. 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.

### 20.5.3.5. TreeBuilder Objects

class `xml.etree.ElementTree.``TreeBuilder`(element_factory=None)

  Generic element structure builder. This builder converts a sequence of start, data, and end 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.

  `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.

  In addition, a custom `TreeBuilder` object can provide the following method:

  `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.

### 20.5.3.6. XMLParser对象

class `xml.etree.ElementTree.``XMLParser`(html=0, 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. The html argument was historically used for backwards compatibility and is now deprecated. If encoding 1 is given, the value overrides the encoding specified in the XML file.

  3.4 版后已移除: The html argument. The remaining arguments should be passed via keyword to prepare for the removal of the html argument.

  `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.

  `doctype`(name, pubid, system)

    3.2 版后已移除: Define the `TreeBuilder.doctype()` method on a custom TreeBuilder target.

  `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)`. `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

### 20.5.3.7. 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"`, `"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.

    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.

  If you need a fully populated element, look for “end” events instead.

  3.4 新版功能.

### 20.5.3.8. 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)

  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.