19.13. xml.etree.ElementTree — The ElementTree XML API
New in version 2.5.
The Element type is a flexible container object, designed to store
hierarchical data structures in memory. The type can be described as a cross
between a list and a dictionary.
Each element has a number of properties associated with it:
- a tag which is a string identifying what kind of data this element represents
(the element type, in other words).
- a number of attributes, stored in a Python dictionary.
- a text string.
- an optional tail string.
- a number of child elements, stored in a Python sequence
To create an element instance, use the Element constructor or the
SubElement() factory function.
The ElementTree class can be used to wrap an element structure, and
convert it from and to XML.
A C implementation of this API is available as xml.etree.cElementTree.
See http://effbot.org/zone/element-index.htm for tutorials and links to other
docs. Fredrik Lundh’s page is also the location of the development version of
the xml.etree.ElementTree.
Changed in version 2.7: The ElementTree API is updated to 1.3. For more information, see
Introducing ElementTree 1.3.
19.13.1. Functions
- 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.
-
xml.etree.ElementTree.dump(elem)
Writes an element tree or element structure to sys.stdout. This function
should be used for debugging only.
The exact output format is implementation dependent. In this version, it’s
written as an ordinary XML file.
elem is an element tree or an individual element.
-
xml.etree.ElementTree.fromstring(text)
- Parses an XML section from a string constant. Same as XML(). text
is a string containing XML data. Returns an Element instance.
-
xml.etree.ElementTree.fromstringlist(sequence, parser=None)
Parses an XML document from a sequence of string fragments. sequence is a
list or other sequence containing XML data fragments. parser is an
optional parser instance. If not given, the standard XMLParser
parser is used. Returns an Element instance.
New in version 2.7.
-
xml.etree.ElementTree.iselement(element)
- Checks if an object appears to be a valid element object. element is an
element instance. Returns a true value if this is an element object.
-
xml.etree.ElementTree.iterparse(source, events=None, parser=None)
Parses an XML section into an element tree incrementally, and reports what’s
going on to the user. source is a filename or file object containing XML
data. events is a list of events to report back. If omitted, only “end”
events are reported. parser is an optional parser instance. If not
given, the standard XMLParser parser is used. Returns an
iterator providing (event, elem) pairs.
Note
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.
-
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.
-
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.
New in version 2.7.
-
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")
- 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). method is either "xml",
"html" or "text" (default is "xml"). Returns an encoded string
containing the XML data.
-
xml.etree.ElementTree.tostringlist(element, encoding="us-ascii", method="xml")
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). method is either "xml",
"html" or "text" (default is "xml"). Returns a list of encoded
strings containing the XML data. It does not guarantee any specific
sequence, except that "".join(tostringlist(element)) ==
tostring(element).
New in version 2.7.
-
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.
19.13.2. Element Objects
-
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
- A string identifying what kind of data this element represents (the
element type, in other words).
-
text
- The text attribute can be used to hold additional data associated with
the element. As the name implies this attribute is usually a string but
may be any application-specific object. If the element is created from
an XML file the attribute will contain any text found between the element
tags.
-
tail
- The tail attribute can be used to hold additional data associated with
the element. This attribute is usually a string but may be any
application-specific object. If the element is created from an XML file
the attribute will contain any text found after the element’s end tag and
before the next tag.
-
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 elements internal list
of subelements.
-
extend(subelements)
Appends subelements from a sequence object with zero or more elements.
Raises AssertionError if a subelement is not a valid object.
New in version 2.7.
-
find(match)
- Finds the first subelement matching match. match may be a tag name
or path. Returns an element instance or None.
-
findall(match)
- Finds all matching subelements, by tag name or path. Returns a list
containing all matching elements in document order.
-
findtext(match, default=None)
- Finds text for the first subelement matching match. match may be
a tag name or 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.
-
getchildren()
Deprecated since version 2.7: Use list(elem) or iteration.
-
getiterator(tag=None)
Deprecated since version 2.7: Use method Element.iter() instead.
-
insert(index, element)
- Inserts a subelement at the given position in this 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.
-
iterfind(match)
Finds all matching subelements, by tag name or path. Returns an iterable
yielding all matching elements in document order.
New in version 2.7.
-
itertext()
Creates a text iterator. The iterator loops over this element and all
subelements, in document order, and returns all inner text.
New in version 2.7.
-
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"
19.13.3. 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)
- Finds the first toplevel element matching match. match may be a tag
name or path. Same as getroot().find(match). Returns the first matching
element, or None if no element was found.
-
findall(match)
- Finds all matching subelements, by tag name or path. Same as
getroot().findall(match). match may be a tag name or path. Returns a
list containing all matching elements, in document order.
-
findtext(match, default=None)
- Finds the element text for the first toplevel element with given tag.
Same as getroot().findtext(match). match may be a tag name or path.
default is the value to return if the element was not found. Returns
the text content of the first matching element, or the default value no
element was found. Note that if the element is found, but has no text
content, this method returns an empty string.
-
getiterator(tag=None)
Deprecated since version 2.7: Use method ElementTree.iter() instead.
-
getroot()
- Returns the root element for this tree.
-
iter(tag=None)
- Creates and returns a tree iterator for the root element. The iterator
loops over all elements in this tree, in section order. tag is the tag
to look for (default is to return all elements)
-
iterfind(match)
Finds all matching subelements, by tag name or path. Same as
getroot().iterfind(match). Returns an iterable yielding all matching
elements in document order.
New in version 2.7.
-
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, method="xml")
- 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 (default is None). method is either
"xml", "html" or "text" (default is "xml"). Returns an
encoded string.
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")
19.13.4. QName Objects
-
class xml.etree.ElementTree.QName(text_or_uri, tag=None)
- QName wrapper. This can be used to wrap a QName attribute value, in order
to get proper namespace handling on output. text_or_uri is a string
containing the QName value, in the form {uri}local, or, if the tag argument
is given, the URI part of a QName. If tag is given, the first argument is
interpreted as an URI, and this argument is interpreted as a local name.
QName instances are opaque.
19.13.5. TreeBuilder Objects
-
class xml.etree.ElementTree.TreeBuilder(element_factory=None)
Generic element structure builder. This builder converts a sequence of
start, data, and end method calls to a well-formed element structure. You
can use this class to build an element structure using a custom XML parser,
or a parser for some other XML-like format. The element_factory is called
to create new Element instances when given.
-
close()
- Flushes the builder buffers, and returns the toplevel document
element. Returns an Element instance.
-
data(data)
- Adds text to the current element. data is a string. This should be
either a bytestring, or a Unicode string.
-
end(tag)
- Closes the current element. tag is the element name. Returns the
closed element.
-
start(tag, attrs)
- Opens a new element. tag is the element name. attrs is a dictionary
containing element attributes. Returns the opened element.
In addition, a custom TreeBuilder object can provide the
following method:
-
doctype(name, pubid, system)
Handles a doctype declaration. name is the doctype name. pubid is
the public identifier. system is the system identifier. This method
does not exist on the default TreeBuilder class.
New in version 2.7.
19.13.6. XMLParser Objects
-
class xml.etree.ElementTree.XMLParser(html=0, target=None, encoding=None)
Element structure builder for XML source data, based on the expat
parser. html are predefined HTML entities. This flag is not supported by
the current implementation. target is the target object. If omitted, the
builder uses an instance of the standard TreeBuilder class. encoding
is optional. If given, the value overrides the encoding specified in the
XML file.
-
close()
- Finishes feeding data to the parser. Returns an element structure.
-
doctype(name, pubid, system)
Deprecated since version 2.7: Define the TreeBuilder.doctype() method on a custom TreeBuilder
target.
-
feed(data)
- Feeds data to the parser. data is encoded data.
XMLParser.feed() calls target‘s start() method
for each opening tag, its end() method for each closing tag,
and data is processed by method data(). XMLParser.close()
calls target‘s method close().
XMLParser can be used not only for building a tree structure.
This is an example of counting the maximum depth of an XML file:
>>> from xml.etree.ElementTree import XMLParser
>>> class MaxDepth: # The target object of the parser
... maxDepth = 0
... depth = 0
... def start(self, tag, attrib): # Called for each opening tag.
... self.depth += 1
... if self.depth > self.maxDepth:
... self.maxDepth = self.depth
... def end(self, tag): # Called for each closing tag.
... self.depth -= 1
... def data(self, data):
... pass # We do not need to do anything with data.
... def close(self): # Called when all data has been parsed.
... return self.maxDepth
...
>>> target = MaxDepth()
>>> parser = XMLParser(target=target)
>>> exampleXml = """
... <a>
... <b>
... </b>
... <b>
... <c>
... <d>
... </d>
... </c>
... </b>
... </a>"""
>>> parser.feed(exampleXml)
>>> parser.close()
4
Footnotes