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19.12. xml.etree.ElementTree — The ElementTree XML API

Source code: Lib/xml/etree/ElementTree.py


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 3.2: The ElementTree API is updated to 1.3. For more information, see Introducing ElementTree 1.3.

19.12.1. Functions

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.

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 3.2.

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 3.2.

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 [1] is the output encoding (default is US-ASCII). Use encoding="unicode" to generate a Unicode string. method is either "xml", "html" or "text" (default is "xml"). Returns an (optionally) 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 [1] is the output encoding (default is US-ASCII). Use encoding="unicode" to generate a Unicode string. method is either "xml", "html" or "text" (default is "xml"). Returns a list of (optionally) encoded strings containing the XML data. It does not guarantee any specific sequence, except that "".join(tostringlist(element)) == tostring(element).

New in version 3.2.

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.

19.12.2. 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 3.2.

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 3.2: Use list(elem) or iteration.

getiterator(tag=None)

Deprecated since version 3.2: 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 3.2.

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 3.2.

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")

19.12.3. 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 3.2: 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 3.2.

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 [1] is the output encoding (default is US-ASCII). Use encoding="unicode" to write a Unicode string. 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). method is either "xml", "html" or "text" (default is "xml"). Returns an (optionally) 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")

19.12.4. 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.

19.12.5. 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 3.2.

19.12.6. 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 [1] 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 3.2: 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

[1]The encoding string included in XML output should conform to the appropriate standards. For example, “UTF-8” is valid, but “UTF8” is not. See http://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl and http://www.iana.org/assignments/character-sets.