>>> 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'
并非XML输入的所有元素都将作为解析树的元素结束。目前，此模块跳过输入中的任何XML注释、处理指令和文档类型声明。然而，使用这个模块的API而不是从XML文本解析构建的树可以包含注释和处理指令，生成XML输出时同样包含这些注释和处理指令。可以通过将自定义 TreeBuilder 实例传递给 XMLParser 构造函数来访问文档类型声明。
Pull API进行非阻塞解析
Most parsing functions provided by this module require the whole document
to be read at once before returning any result. It is possible to use an
XMLParser and feed data into it incrementally, but it is a push API that
calls methods on a callback target, which is too low-level and inconvenient for
most needs. Sometimes what the user really wants is to be able to parse XML
incrementally, without blocking operations, while enjoying the convenience of
fully constructed Element objects.
The most powerful tool for doing this is XMLPullParser. It does not
require a blocking read to obtain the XML data, and is instead fed with data
incrementally with XMLPullParser.feed() calls. To get the parsed XML
elements, call XMLPullParser.read_events(). Here is an example:
>>> parser = ET.XMLPullParser(['start', 'end'])
>>> parser.feed('<mytag>sometext')
>>> list(parser.read_events())
[('start', <Element 'mytag' at 0x7fa66db2be58>)]
>>> parser.feed(' more text</mytag>')
>>> for event, elem in parser.read_events():
... print(event)
... print(elem.tag, 'text=', elem.text)
The obvious use case is applications that operate in a non-blocking fashion
where the XML data is being received from a socket or read incrementally from
some storage device. In such cases, blocking reads are unacceptable.
Because it's so flexible, XMLPullParser can be inconvenient to use for
simpler use-cases. If you don't mind your application blocking on reading XML
data but would still like to have incremental parsing capabilities, take a look
at iterparse(). It can be useful when you're reading a large XML document
and don't want to hold it wholly in memory.
查找感兴趣的元素
Element 有一些很有效的方法，可帮助递归遍历其下的所有子树（包括子级，子级的子级，等等）。例如 Element.iter():
>>> for neighbor in root.iter('neighbor'):
... print(neighbor.attrib)
{'name': 'Austria', 'direction': 'E'}
{'name': 'Switzerland', 'direction': 'W'}
{'name': 'Malaysia', 'direction': 'N'}
{'name': 'Costa Rica', 'direction': 'W'}
{'name': 'Colombia', 'direction': 'E'}
Element.findall() 仅查找当前元素的直接子元素中带有指定标签的元素。 Element.find() 找带有特定标签的 第一个 子级，然后可以用 Element.text 访问元素的文本内容。 Element.get 访问元素的属性:
>>> for country in root.findall('country'):
... rank = country.find('rank').text
... name = country.get('name')
... print(name, rank)
Liechtenstein 1
Singapore 4
Panama 68
通过使用 XPath ，可以更精确地指定要查找的元素。
修改XML文件
ElementTree 提供了一种构建XML文档并将其写入文件的简单方法。调用 ElementTree.write()
方法就可以实现。
创建后可以直接操作 Element 对象。例如：使用 Element.text 修改文本字段，使用 Element.set() 方法添加和修改属性，以及使用 Element.append() 添加新的子元素。
假设我们要为每个国家/地区的中添加一个排名，并在排名元素中添加一个 updated 属性：
>>> for rank in root.iter('rank'):
... new_rank = int(rank.text) + 1
... rank.text = str(new_rank)
... rank.set('updated', 'yes')
>>> tree.write('output.xml')
生成的XML现在看起来像这样：
<?xml version="1.0"?>
<country name="Liechtenstein">
<rank updated="yes">2</rank>
<year>2008</year>
<gdppc>141100</gdppc>
<neighbor name="Austria" direction="E"/>
<neighbor name="Switzerland" direction="W"/>
</country>
<country name="Singapore">
<rank updated="yes">5</rank>
<year>2011</year>
<gdppc>59900</gdppc>
<neighbor name="Malaysia" direction="N"/>
</country>
<country name="Panama">
<rank updated="yes">69</rank>
<year>2011</year>
<gdppc>13600</gdppc>
<neighbor name="Costa Rica" direction="W"/>
<neighbor name="Colombia" direction="E"/>
</country>
</data>
可以使用 Element.remove() 删除元素。假设我们要删除排名高于50的所有国家/地区:
>>> for country in root.findall('country'):
... # using root.findall() to avoid removal during traversal
... rank = int(country.find('rank').text)
... if rank > 50:
... root.remove(country)
>>> tree.write('output.xml')
Note that concurrent modification while iterating can lead to problems,
just like when iterating and modifying Python lists or dicts.
Therefore, the example first collects all matching elements with
root.findall(), and only then iterates over the list of matches.
生成的XML现在看起来像这样：
<?xml version="1.0"?>
<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>
SubElement() 函数还提供了一种便捷方法来为给定元素创建新的子元素:
>>> a = ET.Element('a')
>>> b = ET.SubElement(a, 'b')
>>> c = ET.SubElement(a, 'c')
>>> d = ET.SubElement(c, 'd')
>>> ET.dump(a)
<a><b /><c><d /></c></a>
使用命名空间解析XML
If the XML input has namespaces, tags and attributes
with prefixes in the form prefix:sometag get expanded to
{uri}sometag where the prefix is replaced by the full URI.
Also, if there is a default namespace,
that full URI gets prepended to all of the non-prefixed tags.
Here is an XML example that incorporates two namespaces, one with the
prefix "fictional" and the other serving as the default namespace:
<?xml version="1.0"?>
<actors xmlns:fictional="http://characters.example.com"
xmlns="http://people.example.com">
<actor>
<name>John Cleese</name>
<fictional:character>Lancelot</fictional:character>
<fictional:character>Archie Leach</fictional:character>
</actor>
<actor>
<name>Eric Idle</name>
<fictional:character>Sir Robin</fictional:character>
<fictional:character>Gunther</fictional:character>
<fictional:character>Commander Clement</fictional:character>
</actor>
</actors>
One way to search and explore this XML example is to manually add the
URI to every tag or attribute in the xpath of a
find() or findall():
root = fromstring(xml_text)
for actor in root.findall('{http://people.example.com}actor'):
name = actor.find('{http://people.example.com}name')
print(name.text)
for char in actor.findall('{http://characters.example.com}character'):
print(' |-->', char.text)
A better way to search the namespaced XML example is to create a
dictionary with your own prefixes and use those in the search functions:
ns = {'real_person': 'http://people.example.com',
'role': 'http://characters.example.com'}
for actor in root.findall('real_person:actor', ns):
name = actor.find('real_person:name', ns)
print(name.text)
for char in actor.findall('role:character', ns):
print(' |-->', char.text)
These two approaches both output:
John Cleese
|--> Lancelot
|--> Archie Leach
Eric Idle
|--> Sir Robin
|--> Gunther
|--> Commander Clement
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.
Here's an example that demonstrates some of the XPath capabilities of the
module. We'll be using the countrydata XML document from the
Parsing XML section:
import xml.etree.ElementTree as ET
root = ET.fromstring(countrydata)
# Top-level elements
root.findall(".")
# All 'neighbor' grand-children of 'country' children of the top-level
# elements
root.findall("./country/neighbor")
# Nodes with name='Singapore' that have a 'year' child
root.findall(".//year/..[@name='Singapore']")
# 'year' nodes that are children of nodes with name='Singapore'
root.findall(".//*[@name='Singapore']/year")
# All 'neighbor' nodes that are the second child of their parent
root.findall(".//neighbor[2]")
For XML with namespaces, use the usual qualified {namespace}tag notation:
# All dublin-core "title" tags in the document
root.findall(".//{http://purl.org/dc/elements/1.1/}title")
Selects all child elements with the given tag.
For example, spam selects all child elements
named spam, and spam/egg selects all
grandchildren named egg in all children named
spam. {namespace}* selects all tags in the
given namespace, {*}spam selects tags named
spam in any (or no) namespace, and {}*
only selects tags that are not in a namespace.
在 3.8 版更改: Support for star-wildcards was added.
选择所有子元素，包括注释和处理说明。例如 */egg 选择所有名为 egg 的孙元素。
选择当前节点。这在路径的开头非常有用，用于指示它是相对路径。
Selects all subelements, on all levels beneath the
current element. For example, .//egg selects
all egg elements in the entire tree.
Selects the parent element. Returns None if the
path attempts to reach the ancestors of the start
element (the element find was called on).
[@attrib]
选择具有给定属性的所有元素。
[@attrib='value']
选择给定属性具有给定值的所有元素。该值不能包含引号。
[tag]
选择所有包含 tag 子元素的元素。只支持直系子元素。
[.='text']
选择完整文本内容等于 text 的所有元素（包括后代）。
3.7 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]
Selects all elements that are located at the given
position. The position can be either an integer
(1 is the first position), the expression last()
(for the last position), or a position relative to
the last position (e.g. last()-1).
谓词（方括号内的表达式）之前必须带有标签名称，星号或其他谓词。position 谓词前必须有标签名称。
参考引用
xml.etree.ElementTree.canonicalize(xml_data=None, *, out=None, from_file=None, **options)
C14N 2.0 转换功能。.
Canonicalization is a way to normalise XML output in a way that allows
byte-by-byte comparisons and digital signatures. It reduced the freedom
that XML serializers have and instead generates a more constrained XML
representation. The main restrictions regard the placement of namespace
declarations, the ordering of attributes, and ignorable whitespace.
This function takes an XML data string (xml_data) or a file path or
file-like object (from_file) as input, converts it to the canonical
form, and writes it out using the out file(-like) object, if provided,
or returns it as a text string if not. The output file receives text,
not bytes. It should therefore be opened in text mode with utf-8
encoding.
典型使用:
xml_data = "<root>...</root>"
print(canonicalize(xml_data))
with open("c14n_output.xml", mode='w', encoding='utf-8') as out_file:
canonicalize(xml_data, out=out_file)
with open("c14n_output.xml", mode='w', encoding='utf-8') as out_file:
canonicalize(from_file="inputfile.xml", out=out_file)
The configuration options are as follows:
with_comments: set to true to include comments (default: false)
strip_text: set to true to strip whitespace before and after text content（默认值：否）
exclude_attrs: a set of attribute names that should not be serialised
exclude_tags: a set of tag names that should not be serialised
In the option list above, "a set" refers to any collection or iterable of
strings, no ordering is expected.
3.8 新版功能.
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.
在 3.8 版更改: The dump() function now preserves the attribute order specified
by the user.
xml.etree.ElementTree.fromstring(text, parser=None)
Parses an XML section from a string constant. Same as XML(). text
is a string containing XML data. parser is an optional parser instance.
If not given, the standard XMLParser parser is used.
Returns an Element instance.
xml.etree.ElementTree.fromstringlist(sequence, parser=None)
Parses an XML document from a sequence of string fragments. sequence is a
list or other sequence containing XML data fragments. parser is an
optional parser instance. If not given, the standard XMLParser
parser is used. Returns an Element instance.
3.2 新版功能.
xml.etree.ElementTree.indent(tree, space=" ", level=0)
Appends whitespace to the subtree to indent the tree visually.
This can be used to generate pretty-printed XML output.
tree can be an Element or ElementTree. space is the whitespace
string that will be inserted for each indentation level, two space
characters by default. For indenting partial subtrees inside of an
already indented tree, pass the initial indentation level as level.
3.9 新版功能.
xml.etree.ElementTree.iselement(element)
Check if an object appears to be a valid element object. element is an
element instance. Return True if this is an element object.
xml.etree.ElementTree.iterparse(source, events=None, parser=None)
Parses an XML section into an element tree incrementally, and reports what's
going on to the user. source is a filename or file object
containing XML data. events is a sequence of events to report back. The
supported events are the strings "start", "end", "comment",
"pi", "start-ns" and "end-ns"
(the "ns" events are used to get detailed namespace
information). If events is omitted, only "end" events are reported.
parser is an optional parser instance. If not given, the standard
XMLParser parser is used. parser must be a subclass of
XMLParser and can only use the default TreeBuilder as a
target. Returns an iterator providing (event, elem) pairs.
Note that while iterparse() builds the tree incrementally, it issues
blocking reads on source (or the file it names). As such, it's unsuitable
for applications where blocking reads can't be made. For fully non-blocking
parsing, see XMLPullParser.
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。
在 3.8 版更改: The comment and pi events were added.
xml.etree.ElementTree.parse(source, parser=None)
Parses an XML section into an element tree. source is a filename or file
object containing XML data. parser is an optional parser instance. If
not given, the standard XMLParser parser is used. Returns an
ElementTree instance.
xml.etree.ElementTree.ProcessingInstruction(target, text=None)
PI element factory. This factory function creates a special element that
will be serialized as an XML processing instruction. target is a string
containing the PI target. text is a string containing the PI contents, if
given. Returns an element instance, representing a processing instruction.
Note that XMLParser skips over processing instructions
in the input instead of creating comment objects for them. An
ElementTree will only contain processing instruction nodes if
they have been inserted into to the tree using one of the
Element methods.
xml.etree.ElementTree.register_namespace(prefix, uri)
Registers a namespace prefix. The registry is global, and any existing
mapping for either the given prefix or the namespace URI will be removed.
prefix is a namespace prefix. uri is a namespace uri. Tags and
attributes in this namespace will be serialized with the given prefix, if at
all possible.
3.2 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", *, 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 is
the output encoding (default is US-ASCII). Use encoding="unicode" to
generate a Unicode string (otherwise, a bytestring is generated). method
is either "xml", "html" or "text" (default is "xml").
xml_declaration, default_namespace and short_empty_elements has the same
meaning as in ElementTree.write(). Returns an (optionally) encoded string
containing the XML data.
3.4 新版功能: short_empty_elements 形参。
3.8 新版功能: The xml_declaration and default_namespace parameters.
在 3.8 版更改: The tostring() function now preserves the attribute order
specified by the user.
xml.etree.ElementTree.tostringlist(element, encoding="us-ascii", method="xml", *, xml_declaration=None, default_namespace=None, short_empty_elements=True)
Generates a string representation of an XML element, including all
subelements. element is an Element instance. encoding 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 新版功能.
3.4 新版功能: short_empty_elements 形参。
3.8 新版功能: The xml_declaration and default_namespace parameters.
在 3.8 版更改: 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.
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">
</document>
结果可能如下所示：
<document xmlns:xi="http://www.w3.org/2001/XInclude">
</document>
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 新版功能: The base_url and max_depth parameters.
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)。
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.
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.
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)
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.
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 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.
<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
<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")
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.
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.
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.
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 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.
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()
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.
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.
在 3.8 版更改: The comment and pi events were added.
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.
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.
