xml.etree.ElementTree — ElementTree XML API ¶

XML 树和元素 ¶

XML is an inherently hierarchical data format, and the most natural way to represent it is with a tree. ET has two classes for this purpose - ElementTree represents the whole XML document as a tree, and Element represents a single node in this tree. Interactions with the whole document (reading and writing to/from files) are usually done on the ElementTree level. Interactions with a single XML element and its sub-elements are done on the Element level.

剖析 XML ¶

We’ll be using the following XML document as the sample data for this section:

<?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>
									

We can import this data by reading from a file:

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

Or directly from a string:

root = ET.fromstring(country_data_as_string)
									

fromstring() parses XML from a string directly into an Element , which is the root element of the parsed tree. Other parsing functions may create an ElementTree . Check the documentation to be sure.

As an Element , root has a tag and a dictionary of attributes:

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

It also has children nodes over which we can iterate:

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

Children are nested, and we can access specific child nodes by index:

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

Pull API for non-blocking parsing ¶

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 对象。

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.

Finding interesting elements ¶

Element has some useful methods that help iterate recursively over all the sub-tree below it (its children, their children, and so on). For example, 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() finds only elements with a tag which are direct children of the current element. Element.find() finds the first child with a particular tag, and Element.text accesses the element’s text content. Element.get() accesses the element’s attributes:

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

More sophisticated specification of which elements to look for is possible by using XPath .

修改 XML 文件 ¶

ElementTree provides a simple way to build XML documents and write them to files. ElementTree.write() method serves this purpose.

Once created, an Element object may be manipulated by directly changing its fields (such as Element.text ), adding and modifying attributes ( Element.set() method), as well as adding new children (for example with Element.append() ).

Let’s say we want to add one to each country’s rank, and add an updated attribute to the rank element:

>>> 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')
									

Our XML now looks like this:

<?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>
									

We can remove elements using Element.remove() . Let’s say we want to remove all countries with a rank higher than 50:

>>> 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.

Our XML now looks like this:

<?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() function also provides a convenient way to create new sub-elements for a given element:

>>> 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>
									

Parsing XML with Namespaces ¶

If the XML input has 名称空间 , tags and attributes with prefixes in the form prefix:sometag get expanded to {uri}sometag 在哪里 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
									

Additional resources ¶

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

范例 ¶

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

import xml.etree.ElementTree as ET
root = ET.fromstring(countrydata)
# Top-level elements
root.findall(".")
# All 'neighbor' grand-children of 'country' children of the top-level
# elements
root.findall("./country/neighbor")
# Nodes with name='Singapore' that have a 'year' child
root.findall(".//year/..[@name='Singapore']")
# 'year' nodes that are children of nodes with name='Singapore'
root.findall(".//*[@name='Singapore']/year")
# All 'neighbor' nodes that are the second child of their parent
root.findall(".//neighbor[2]")
									

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

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

支持 XPath 句法 ¶

Predicates (expressions within square brackets) must be preceded by a tag name, an asterisk, or another predicate. position predicates must be preceded by a tag name.

函数 ¶

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

C14N 2.0 transformation function.

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 编码。

Typical uses:

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 选项 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

  (default: false)

• rewrite_prefixes : set to true to replace namespace prefixes by “n{number}”

  (default: false)

• qname_aware_tags : a set of qname aware tag names in which prefixes

  should be replaced in text content (default: empty)

• qname_aware_attrs : a set of qname aware attribute names in which prefixes

  should be replaced in text content (default: empty)

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

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

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

3.8 版新增。

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.

注意， 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 方法。

xml.etree.ElementTree. dump ( elem ) ¶

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

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

elem is an element tree or an individual element.

3.8 版改变： 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 实例。

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 实例。

3.2 版新增。

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

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

3.9 版新增。

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 文件对象 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.

注意，当 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 .

注意

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.

从 3.4 版起弃用： parser 自变量。

3.8 版改变： 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 实例。

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.

注意， 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 方法。

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

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

3.2 版新增。

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 是 Element 实例。 encoding 1 is the output encoding (default is US-ASCII). Use encoding="unicode" to generate a Unicode string (otherwise, a bytestring is generated). 方法 是 "xml" , "html" or "text" (default is "xml" ). xml_declaration , default_namespace and short_empty_elements has the same meaning as in ElementTree.write() . Returns an (optionally) encoded string containing the XML data.

3.4 版新增： short_empty_elements 参数。

3.8 版新增： xml_declaration and default_namespace 参数。

3.8 版改变： 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 是 Element 实例。 encoding 1 is the output encoding (default is US-ASCII). Use encoding="unicode" to generate a Unicode string (otherwise, a bytestring is generated). 方法 是 "xml" , "html" or "text" (default is "xml" ). xml_declaration , default_namespace and short_empty_elements has the same meaning as in ElementTree.write() . Returns a list of (optionally) encoded strings containing the XML data. It does not guarantee any specific sequence, except that b"".join(tostringlist(element)) == tostring(element) .

3.2 版新增。

3.4 版新增： short_empty_elements 参数。

3.8 版新增： xml_declaration and default_namespace 参数。

3.8 版改变： 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 实例。

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.

范例 ¶

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

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

默认情况下， 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 模块：

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>
									

若 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>
									

The result might look something like:

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

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. 包括 ( elem , loader=None , base_url=None , max_depth=6 ) ¶

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

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

3.9 版新增： base_url and max_depth 参数。

元素对象 ¶

class xml.etree.ElementTree. 元素 ( 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 ¶

A string identifying what kind of data this element represents (the element type, in other words).

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 ，和 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>
													

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

To collect the inner text of an element, see itertext() ，例如 "".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 ) ¶

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

3.2 版新增。

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 . 名称空间 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. 名称空间 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. 名称空间 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 ) ¶

插入 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 不是 None or '*' , only elements whose tag equals tag are returned from the iterator. If the tree structure is modified during iteration, the result is undefined.

3.2 版新增。

iterfind ( match , namespaces=None ) ¶

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

3.2 版新增。

itertext ( ) ¶

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

3.2 版新增。

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 ) ¶

移除 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() 函数。

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 Objects ¶

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 ) ¶

如同 Element.find() , starting at the root of the tree.

findall ( match , namespaces=None ) ¶

如同 Element.findall() , starting at the root of the tree.

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

如同 Element.findtext() , starting at the root of the tree.

getroot ( ) ¶

Returns the root element for this tree.

iter ( tag=None ) ¶

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

iterfind ( match , namespaces=None ) ¶

如同 Element.iterfind() , starting at the root of the tree.

3.2 版新增。

parse ( source , parser=None ) ¶

Loads an external XML section into this element tree. source is a file name or 文件对象 . 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 文件对象 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”). 方法 是 "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 自变量。若 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 文件对象 ; make sure you do not try to write a string to a binary stream and vice versa.

3.4 版新增： short_empty_elements 参数。

3.8 版改变： 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.

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 实例。

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 。若 insert_comments is true, this will also add it to the tree.

3.8 版新增。

pi ( target , text ) ¶

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

3.8 版新增。

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 类。

3.2 版新增。

start_ns ( prefix , uri ) ¶

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

3.8 版新增。

end_ns ( prefix ) ¶

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

3.8 版新增。

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 函数。

3.8 版新增。

XMLParser 对象 ¶

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

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

3.8 版改变： Parameters are now 仅关键词 . html argument no longer supported.

close ( ) ¶

Finishes feeding data to the parser. Returns the result of calling the close() 方法在 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() 调用 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 类。 XMLParser.close() 调用 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 Objects ¶

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" ) 和 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.

注意

XMLPullParser only guarantees that it has seen the “>” character of a starting tag when it emits a “start” event, so the attributes are defined, but the contents of the text and tail attributes are undefined at that point. The same applies to the element children; they may or may not be present.

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

3.4 版新增。

3.8 版改变： comment and pi events were added.

异常 ¶

class xml.etree.ElementTree. ParseError ¶

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

code ¶

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

position ¶

元组 line , column numbers, specifying where the error occurred.

脚注

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 .