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diff --git a/Doc/library/xml.etree.elementtree.rst b/Doc/library/xml.etree.elementtree.rst index c5c8802..782ebe7 100644 --- a/Doc/library/xml.etree.elementtree.rst +++ b/Doc/library/xml.etree.elementtree.rst @@ -5,49 +5,232 @@ :synopsis: Implementation of the ElementTree API. .. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com> -**Source code:** :source:`Lib/xml/etree/ElementTree.py` +The :mod:`xml.etree.ElementTree` module implements a simple and efficient API +for parsing and creating XML data. + +.. versionchanged:: 3.3 + This module will use a fast implementation whenever available. + The :mod:`xml.etree.cElementTree` module is deprecated. + +Tutorial +-------- + +This is a short tutorial for using :mod:`xml.etree.ElementTree` (``ET`` in +short). The goal is to demonstrate some of the building blocks and basic +concepts of the module. + +XML tree and elements +^^^^^^^^^^^^^^^^^^^^^ + +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 - +:class:`ElementTree` represents the whole XML document as a tree, and +:class:`Element` represents a single node in this tree. Interactions with +the whole document (reading and writing to/from files) are usually done +on the :class:`ElementTree` level. Interactions with a single XML element +and its sub-elements are done on the :class:`Element` level. + +.. _elementtree-parsing-xml: + +Parsing XML +^^^^^^^^^^^ + +We'll be using the following XML document contained in a Python string as the +sample data for this section:: + + countrydata = r'''<?xml version="1.0"?> + <data> + <country name="Liechtenshtein"> + <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> + ''' + +First, import the module and parse the data:: + + import xml.etree.ElementTree as ET + + root = ET.fromstring(countrydata) + +:func:`fromstring` parses XML from a string directly into an :class:`Element`, +which is the root element of the parsed tree. Other parsing functions may +create an :class:`ElementTree`. Make sure to check the documentation to be +sure. + +As an :class:`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': 'Liechtenshtein'} + country {'name': 'Singapore'} + country {'name': 'Panama'} + +Children are nested, and we can access specific child nodes by index:: + + >>> root[0][1].text + '2008' + +Finding interesting elements +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +:class:`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, +:meth:`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'} + +More sophisticated specification of which elements to look for is possible by +using :ref:`XPath <elementtree-xpath>`. + +Building XML documents +^^^^^^^^^^^^^^^^^^^^^^ + +``ET`` provides a simple way to build XML documents and write them to files. +The :meth:`ElementTree.write` method serves this purpose. + +Once created, an :class:`Element` object may be manipulated by directly changing +its fields (such as :attr:`Element.text`), adding and modifying attributes +(:meth:`Element.set` method), as well as adding new children (for example +with :meth:`Element.append`). + +The :func:`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> + +Additional resources +^^^^^^^^^^^^^^^^^^^^ --------------- - -The :class:`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 :class:`Element` constructor or the -:func:`SubElement` factory function. - -The :class:`ElementTree` class can be used to wrap an element structure, and -convert it from and to XML. +See http://effbot.org/zone/element-index.htm for tutorials and links to other +docs. -A C implementation of this API is available as :mod:`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. +.. _elementtree-xpath: -.. versionchanged:: 3.2 - The ElementTree API is updated to 1.3. For more information, see - `Introducing ElementTree 1.3 - <http://effbot.org/zone/elementtree-13-intro.htm>`_. +XPath support +------------- +This module provides limited support for +`XPath expressions <http://www.w3.org/TR/xpath>`_ 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. + +Example +^^^^^^^ + +Here's an example that demonstrates some of the XPath capabilities of the +module. We'll be using the ``countrydata`` XML document from the +:ref:`Parsing XML <elementtree-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]") + +Supported XPath syntax +^^^^^^^^^^^^^^^^^^^^^^ + ++-----------------------+------------------------------------------------------+ +| Syntax | Meaning | ++=======================+======================================================+ +| ``tag`` | Selects all child elements with the given tag. | +| | For example, ``spam`` selects all child elements | +| | named ``spam``, ``spam/egg`` selects all | +| | grandchildren named ``egg`` in all children named | +| | ``spam``. | ++-----------------------+------------------------------------------------------+ +| ``*`` | Selects all child elements. For example, ``*/egg`` | +| | selects all grandchildren named ``egg``. | ++-----------------------+------------------------------------------------------+ +| ``.`` | 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, ``.//egg`` selects | +| | all ``egg`` elements in the entire tree. | ++-----------------------+------------------------------------------------------+ +| ``..`` | Selects the parent element. | ++-----------------------+------------------------------------------------------+ +| ``[@attrib]`` | Selects all elements that have the given attribute. | ++-----------------------+------------------------------------------------------+ +| ``[@attrib='value']`` | Selects all elements for which the given attribute | +| | has the given value. The value cannot contain | +| | quotes. | ++-----------------------+------------------------------------------------------+ +| ``[tag]`` | Selects all elements that have a child named | +| | ``tag``. Only immediate children are supported. | ++-----------------------+------------------------------------------------------+ +| ``[position]`` | Selects all elements that are located at the given | +| | position. The position can be either an integer | +| | (1 is the first position), the expression ``last()`` | +| | (for the last position), or a position relative to | +| | the last position (e.g. ``last()-1``). | ++-----------------------+------------------------------------------------------+ + +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. + +Reference +--------- .. _elementtree-functions: Functions ---------- +^^^^^^^^^ .. function:: Comment(text=None) @@ -198,8 +381,7 @@ Functions .. _elementtree-element-objects: Element Objects ---------------- - +^^^^^^^^^^^^^^^ .. class:: Element(tag, attrib={}, **extra) @@ -281,36 +463,43 @@ Element Objects .. method:: append(subelement) - Adds the element *subelement* to the end of this elements internal list - of subelements. + Adds the element *subelement* to the end of this element's internal list + of subelements. Raises :exc:`TypeError` if *subelement* is not an + :class:`Element`. .. method:: extend(subelements) Appends *subelements* from a sequence object with zero or more elements. - Raises :exc:`AssertionError` if a subelement is not a valid object. + Raises :exc:`TypeError` if a subelement is not an :class:`Element`. .. versionadded:: 3.2 - .. method:: find(match) + .. method:: find(match, namespaces=None) Finds the first subelement matching *match*. *match* may be a tag name - or path. Returns an element instance or ``None``. + or a :ref:`path <elementtree-xpath>`. Returns an element instance + or ``None``. *namespaces* is an optional mapping from namespace prefix + to full name. - .. method:: findall(match) + .. method:: findall(match, namespaces=None) - Finds all matching subelements, by tag name or path. Returns a list - containing all matching elements in document order. + Finds all matching subelements, by tag name or + :ref:`path <elementtree-xpath>`. Returns a list containing all matching + elements in document order. *namespaces* is an optional mapping from + namespace prefix to full name. - .. method:: findtext(match, default=None) + .. method:: findtext(match, default=None, namespaces=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. + a tag name or a :ref:`path <elementtree-xpath>`. 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. .. method:: getchildren() @@ -325,9 +514,10 @@ Element Objects Use method :meth:`Element.iter` instead. - .. method:: insert(index, element) + .. method:: insert(index, subelement) - Inserts a subelement at the given position in this element. + Inserts *subelement* at the given position in this element. Raises + :exc:`TypeError` if *subelement* is not an :class:`Element`. .. method:: iter(tag=None) @@ -341,10 +531,13 @@ Element Objects .. versionadded:: 3.2 - .. method:: iterfind(match) + .. method:: iterfind(match, namespaces=None) + + Finds all matching subelements, by tag name or + :ref:`path <elementtree-xpath>`. Returns an iterable yielding all + matching elements in document order. *namespaces* is an optional mapping + from namespace prefix to full name. - Finds all matching subelements, by tag name or path. Returns an iterable - yielding all matching elements in document order. .. versionadded:: 3.2 @@ -389,7 +582,7 @@ Element Objects .. _elementtree-elementtree-objects: ElementTree Objects -------------------- +^^^^^^^^^^^^^^^^^^^ .. class:: ElementTree(element=None, file=None) @@ -409,28 +602,19 @@ ElementTree Objects care. *element* is an element instance. - .. method:: find(match) + .. method:: find(match, namespaces=None) - 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. + Same as :meth:`Element.find`, starting at the root of the tree. - .. method:: findall(match) + .. method:: findall(match, namespaces=None) - 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. + Same as :meth:`Element.findall`, starting at the root of the tree. - .. method:: findtext(match, default=None) + .. method:: findtext(match, default=None, namespaces=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. + Same as :meth:`Element.findtext`, starting at the root of the tree. .. method:: getiterator(tag=None) @@ -451,11 +635,9 @@ ElementTree Objects to look for (default is to return all elements) - .. method:: iterfind(match) + .. method:: iterfind(match, namespaces=None) - Finds all matching subelements, by tag name or path. Same as - getroot().iterfind(match). Returns an iterable yielding all matching - elements in document order. + Same as :meth:`Element.iterfind`, starting at the root of the tree. .. versionadded:: 3.2 @@ -464,20 +646,29 @@ ElementTree Objects Loads an external XML section into this element tree. *source* is a file name or :term:`file object`. *parser* is an optional parser instance. - If not given, the standard XMLParser parser is used. Returns the section - root element. + If not given, the standard :class:`XMLParser` parser is used. Returns the + section root element. - .. method:: write(file, encoding="us-ascii", xml_declaration=None, method="xml") + .. method:: 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 - :term:`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. + :term:`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``). + *method* is either ``"xml"``, ``"html"`` or ``"text"`` (default is + ``"xml"``). + + The output is either a string (:class:`str`) or binary (:class:`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 + :term:`file object`; make sure you do not try to write a string to a + binary stream and vice versa. + This is the XML file that is going to be manipulated:: @@ -510,7 +701,7 @@ Example of changing the attribute "target" of every link in first paragraph:: .. _elementtree-qname-objects: QName Objects -------------- +^^^^^^^^^^^^^ .. class:: QName(text_or_uri, tag=None) @@ -526,7 +717,7 @@ QName Objects .. _elementtree-treebuilder-objects: TreeBuilder Objects -------------------- +^^^^^^^^^^^^^^^^^^^ .. class:: TreeBuilder(element_factory=None) @@ -534,9 +725,9 @@ TreeBuilder Objects 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 :class:`Element` instances when given. - + 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. .. method:: close() @@ -577,7 +768,7 @@ TreeBuilder Objects .. _elementtree-xmlparser-objects: XMLParser Objects ------------------ +^^^^^^^^^^^^^^^^^ .. class:: XMLParser(html=0, target=None, encoding=None) @@ -585,9 +776,9 @@ XMLParser Objects :class:`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. + builder uses an instance of the standard :class:`TreeBuilder` class. + *encoding* [1]_ is optional. If given, the value overrides the encoding + specified in the XML file. .. method:: close() @@ -645,6 +836,24 @@ This is an example of counting the maximum depth of an XML file:: >>> parser.close() 4 +Exceptions +^^^^^^^^^^ + +.. class:: 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: + + .. attribute:: code + + A numeric error code from the expat parser. See the documentation of + :mod:`xml.parsers.expat` for the list of error codes and their meanings. + + .. attribute:: position + + A tuple of *line*, *column* numbers, specifying where the error occurred. .. rubric:: Footnotes |