xml.etree.cElementTree --- ElementTree XML API¶原始碼：Lib/xml/etree/ElementTree.py
The xml.etree.ElementTree module implements a simple and efficient API
for parsing and creating XML data.
在 3.3 版的變更: This module will use a fast implementation whenever available.
在 3.3 版之後被棄用: xml.etree.cElementTree 模組已被棄用。
備註
如果你需要剖析不受信任或未經驗證的資料，請參閱 XML 安全性。
This is a short tutorial for using xml.etree.ElementTree (ET in
short). The goal is to demonstrate some of the building blocks and basic
concepts of the module.
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.
We'll be using the fictive country_data.xml 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'
備註
Not all elements of the XML input will end up as elements of the
parsed tree. Currently, this module skips over any XML comments,
processing instructions, and document type declarations in the
input. Nevertheless, trees built using this module's API rather
than parsing from XML text can have comments and processing
instructions in them; they will be included when generating XML
output. A document type declaration may be accessed by passing a
custom TreeBuilder instance to the XMLParser
constructor.
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
mytag text= sometext more 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.
Where immediate feedback through events is wanted, calling method
XMLPullParser.flush() can help reduce delay;
please make sure to study the related security notes.
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.
ElementTree provides a simple way to build XML documents and write them to files.
The 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')
XML 現在看起來像這樣：
<?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'):
... # 使用 root.findall() 來避免在遍歷時移除
... 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.
XML 現在看起來像這樣：
<?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>
The 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>
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
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")
語法 |
意義 |
|---|---|
|
Selects all child elements with the given tag.
For example, 在 3.8 版的變更: 新增對星號萬用字元的支援。 |
|
Selects all child elements, including comments and
processing instructions. For example, |
|
Selects the current node. This is mostly useful at the beginning of the path, to indicate that it's a relative path. |
|
Selects all subelements, on all levels beneath the
current element. For example, |
|
Selects the parent element. Returns |
|
選擇所有具有給定屬性的元素。 |
|
Selects all elements for which the given attribute has the given value. The value cannot contain quotes. |
|
Selects all elements for which the given attribute does not have the given value. The value cannot contain quotes. 在 3.10 版被加入. |
|
Selects all elements that have a child named
|
|
Selects all elements whose complete text content,
including descendants, equals the given 在 3.7 版被加入. |
|
Selects all elements whose complete text content,
including descendants, does not equal the given
在 3.10 版被加入. |
|
Selects all elements that have a child named
|
|
Selects all elements that have a child named
在 3.10 版被加入. |
|
Selects all elements that are located at the given
position. The position can be either an integer
(1 is the first position), the expression |
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.
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 reduces 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.
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 options are as follows:
with_comments: set to true to include comments (default: false)
(default: false)
(default: false)
should be replaced in text content (default: empty)
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.
在 3.8 版被加入.
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.
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 版的變更: The dump() function now preserves the attribute order specified
by the user.
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.
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.
在 3.2 版被加入.
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.
在 3.9 版被加入.
Check if an object appears to be a valid element object. element is an
element instance. Return True if this is an element object.
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;
it has a root attribute that references the root element of the
resulting XML tree once source is fully read.
The iterator has the close() method that closes the internal
file object if source is a filename.
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.
備註
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.
在 3.4 版之後被棄用: parser 引數。
在 3.8 版的變更: 新增 context 與 check_hostname 事件。
在 3.13 版的變更: 新增 close() 方法。
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.
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 PI 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.
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.
在 3.2 版被加入.
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.
Generates a string representation of an XML element, including all
subelements. element is an Element instance. encoding [1] is
the output encoding (default is US-ASCII). Use encoding="unicode" to
generate a Unicode string (otherwise, a bytestring is generated). method
is either "xml", "html" or "text" (default is "xml").
xml_declaration, default_namespace and short_empty_elements has the same
meaning as in ElementTree.write(). Returns an (optionally) encoded string
containing the XML data.
在 3.4 版的變更: 新增 short_empty_elements 參數。
在 3.8 版的變更: 新增 xml_declaration 與 default_namespace 參數。
在 3.8 版的變更: The tostring() function now preserves the attribute order
specified by the user.
Generates a string representation of an XML element, including all
subelements. element is an Element instance. encoding [1] is
the output encoding (default is US-ASCII). Use encoding="unicode" to
generate a Unicode string (otherwise, a bytestring is generated). method
is either "xml", "html" or "text" (default is "xml").
xml_declaration, default_namespace and short_empty_elements has the same
meaning as in ElementTree.write(). Returns a list of (optionally) encoded
strings containing the XML data. It does not guarantee any specific sequence,
except that b"".join(tostringlist(element)) == tostring(element).
在 3.2 版被加入.
在 3.4 版的變更: 新增 short_empty_elements 參數。
在 3.8 版的變更: 新增 xml_declaration 與 default_namespace 參數。
在 3.8 版的變更: The tostringlist() function now preserves the attribute order
specified by the user.
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.
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.
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">
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>
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 Element instance.
If the parse mode is "text", this is a string.
If the loader fails, it can return None or raise an exception.
This function expands XInclude directives in-place in tree pointed by elem.
elem is either the root Element or an
ElementTree instance to find such 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 None to disable the limitation.
在 3.9 版的變更: 新增 base_url 與 max_depth 參數。
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.
A string identifying what kind of data this element represents (the element type, in other words).
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.
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.
Resets an element. This function removes all subelements, clears all
attributes, and sets the text and tail attributes to None.
Gets the element attribute named key.
Returns the attribute value, or default if the attribute was not found.
Returns the element attributes as a sequence of (name, value) pairs. The attributes are returned in an arbitrary order.
Returns the elements attribute names as a list. The names are returned in an arbitrary order.
Set the attribute key on the element to value.
The following methods work on the element's children (subelements).
Adds the element subelement to the end of this element's internal list
of subelements. Raises TypeError if subelement is not an
Element.
Appends subelements from an iterable of elements.
Raises TypeError if a subelement is not an Element.
在 3.2 版被加入.
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.
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.
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.
Inserts subelement at the given position in this element. Raises
TypeError if subelement is not an Element.
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.
在 3.2 版被加入.
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.
在 3.2 版被加入.
Creates a text iterator. The iterator loops over this element and all subelements, in document order, and returns all inner text.
在 3.2 版被加入.
Creates a new element object of the same type as this element. Do not
call this method, use the SubElement() factory function instead.
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. In a future
release of Python, all elements will test as True regardless of whether
subelements exist. Instead, prefer explicit len(elem) or
elem is not None tests.:
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")
在 3.12 版的變更: Testing the truth value of an Element emits DeprecationWarning.
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:
# 調整屬性順序，例如排序
attribs = sorted(attrib.items())
attrib.clear()
attrib.update(attribs)
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.
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.
Same as Element.find(), starting at the root of the tree.
Same as Element.findall(), starting at the root of the tree.
Same as Element.findtext(), starting at the root of the tree.
Returns the root element for this tree.
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).
Same as Element.iterfind(), starting at the root of the tree.
在 3.2 版被加入.
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.
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.
在 3.4 版的變更: 新增 short_empty_elements 參數。
在 3.8 版的變更: The write() method now preserves the attribute order specified
by the user.
This is the XML file that is going to be manipulated:
<html>
<head>
<title>Example page</title>
</head>
<body>
<p>Moved to <a href="http://example.org/">example.org</a>
or <a href="http://example.com/">example.com</a>.</p>
</body>
</html>
Example of changing the attribute "target" of every link in first paragraph:
>>> from xml.etree.ElementTree import ElementTree
>>> tree = ElementTree()
>>> tree.parse("index.xhtml")
<Element 'html' at 0xb77e6fac>
>>> p = tree.find("body/p") # Finds first occurrence of tag p in body
>>> p
<Element 'p' at 0xb77ec26c>
>>> links = list(p.iter("a")) # Returns list of all links
>>> links
[<Element 'a' at 0xb77ec2ac>, <Element 'a' at 0xb77ec1cc>]
>>> for i in links: # Iterates through all found links
... i.attrib["target"] = "blank"
...
>>> tree.write("output.xhtml")
QName 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.
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).
Flushes the builder buffers, and returns the toplevel document
element. Returns an Element instance.
Adds text to the current element. data is a string. This should be either a bytestring, or a Unicode string.
Closes the current element. tag is the element name. Returns the closed element.
Opens a new element. tag is the element name. attrs is a dictionary containing element attributes. Returns the opened element.
Creates a comment with the given text. If insert_comments is true,
this will also add it to the tree.
在 3.8 版被加入.
Creates a process instruction with the given target name and text.
If insert_pis is true, this will also add it to the tree.
在 3.8 版被加入.
In addition, a custom TreeBuilder object can provide the
following methods:
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.
在 3.2 版被加入.
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.
在 3.8 版被加入.
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.
在 3.8 版被加入.
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.
在 3.8 版被加入.
This class is the low-level building block of the module. It uses
xml.parsers.expat for efficient, event-based parsing of XML. It can
be fed XML data incrementally with the feed() method, and parsing
events are translated to a push API - by invoking callbacks on the target
object. If target is omitted, the standard TreeBuilder is used.
If encoding [1] is given, the value overrides the
encoding specified in the XML file.
在 3.8 版的變更: Parameters are now keyword-only. The html argument is no longer supported.
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.
Feeds data to the parser. data is encoded data.
Triggers parsing of any previously fed unparsed data, which can be
used to ensure more immediate feedback, in particular with Expat >=2.6.0.
The implementation of flush() temporarily disables reparse deferral
with Expat (if currently enabled) and triggers a reparse.
Disabling reparse deferral has security consequences; please see
xml.parsers.expat.xmlparser.SetReparseDeferralEnabled() for details.
Note that flush() has been backported to some prior releases of
CPython as a security fix. Check for availability of flush()
using hasattr() if used in code running across a variety of Python
versions.
在 3.13 版被加入.
XMLParser.feed() calls target's start(tag, attrs_dict) method
for each opening tag, its end(tag) method for each closing tag, and data
is processed by method data(data). For further supported callback
methods, see the TreeBuilder class. XMLParser.close() calls
target's method close(). XMLParser can be used not only for
building a tree structure. This is an example of counting the maximum depth
of an XML file:
>>> from xml.etree.ElementTree import XMLParser
>>> class MaxDepth: # The target object of the parser
... maxDepth = 0
... depth = 0
... def start(self, tag, attrib): # Called for each opening tag.
... self.depth += 1
... if self.depth > self.maxDepth:
... self.maxDepth = self.depth
... def end(self, tag): # Called for each closing tag.
... self.depth -= 1
... def data(self, data):
... pass # We do not need to do anything with data.
... def close(self): # Called when all data has been parsed.
... return self.maxDepth
...
>>> target = MaxDepth()
>>> parser = XMLParser(target=target)
>>> exampleXml = """
... <a>
... <b>
... </b>
... <b>
... <c>
... <d>
... </d>
... </c>
... </b>
... </a>"""
>>> parser.feed(exampleXml)
>>> parser.close()
4
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 the given bytes data to the parser.
Triggers parsing of any previously fed unparsed data, which can be
used to ensure more immediate feedback, in particular with Expat >=2.6.0.
The implementation of flush() temporarily disables reparse deferral
with Expat (if currently enabled) and triggers a reparse.
Disabling reparse deferral has security consequences; please see
xml.parsers.expat.xmlparser.SetReparseDeferralEnabled() for details.
Note that flush() has been backported to some prior releases of
CPython as a security fix. Check for availability of flush()
using hasattr() if used in code running across a variety of Python
versions.
在 3.13 版被加入.
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().
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：目前的 Element。
comment, pi: the current comment / processing instruction
start-ns: a tuple (prefix, uri) naming the declared namespace
mapping.
end-ns: None (this may change in a future version)
Events provided in a previous call to read_events() will not be
yielded again. Events are consumed from the internal queue only when
they are retrieved from the iterator, so multiple readers iterating in
parallel over iterators obtained from read_events() will have
unpredictable results.
備註
XMLPullParser only guarantees that it has seen the ">"
character of a starting tag when it emits a "start" event, so the
attributes are defined, but the contents of the text and tail attributes
are undefined at that point. The same applies to the element children;
they may or may not be present.
If you need a fully populated element, look for "end" events instead.
在 3.4 版被加入.
在 3.8 版的變更: 新增 context 與 check_hostname 事件。
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:
A numeric error code from the expat parser. See the documentation of
xml.parsers.expat for the list of error codes and their meanings.
A tuple of line, column numbers, specifying where the error occurred.
註解