xml.dom.minidom
— 最小 DOM (文档对象模型) 实现
¶
xml.dom.minidom
is a minimal implementation of the Document Object Model interface, with an API similar to that in other languages. It is intended to be simpler than the full DOM and also significantly smaller. Users who are not already proficient with the DOM should consider using the
xml.etree.ElementTree
module for their XML processing instead.
警告
xml.dom.minidom
module is not secure against maliciously constructed data. If you need to parse untrusted or unauthenticated data see
XML vulnerabilities
.
DOM applications typically start by parsing some XML into a DOM. With
xml.dom.minidom
, this is done through the parse functions:
from xml.dom.minidom import parse, parseString
dom1 = parse('c:\\temp\\mydata.xml') # parse an XML file by name
datasource = open('c:\\temp\\mydata.xml')
dom2 = parse(datasource) # parse an open file
dom3 = parseString('<myxml>Some data<empty/> some more data</myxml>')
parse()
function can take either a filename or an open file object.
xml.dom.minidom.
parse
(
filename_or_file
,
parser=None
,
bufsize=None
)
¶
返回
Document
from the given input.
filename_or_file
may be either a file name, or a file-like object.
parser
, if given, must be a SAX2 parser object. This function will change the document handler of the parser and activate namespace support; other parser configuration (like setting an entity resolver) must have been done in advance.
If you have XML in a string, you can use the
parseString()
function instead:
xml.dom.minidom.
parseString
(
string
,
parser=None
)
¶
返回
Document
that represents the
string
. This method creates an
io.StringIO
object for the string and passes that on to
parse()
.
Both functions return a
Document
object representing the content of the document.
What the
parse()
and
parseString()
functions do is connect an XML parser with a “DOM builder” that can accept parse events from any SAX parser and convert them into a DOM tree. The name of the functions are perhaps misleading, but are easy to grasp when learning the interfaces. The parsing of the document will be completed before these functions return; it’s simply that these functions do not provide a parser implementation themselves.
You can also create a
Document
by calling a method on a “DOM Implementation” object. You can get this object either by calling the
getDOMImplementation()
function in the
xml.dom
package or the
xml.dom.minidom
module. Once you have a
Document
, you can add child nodes to it to populate the DOM:
from xml.dom.minidom import getDOMImplementation
impl = getDOMImplementation()
newdoc = impl.createDocument(None, "some_tag", None)
top_element = newdoc.documentElement
text = newdoc.createTextNode('Some textual content.')
top_element.appendChild(text)
Once you have a DOM document object, you can access the parts of your XML document through its properties and methods. These properties are defined in the DOM specification. The main property of the document object is the
documentElement
property. It gives you the main element in the XML document: the one that holds all others. Here is an example program:
dom3 = parseString("<myxml>Some data</myxml>")
assert dom3.documentElement.tagName == "myxml"
When you are finished with a DOM tree, you may optionally call the
unlink()
method to encourage early cleanup of the now-unneeded objects.
unlink()
是
xml.dom.minidom
-specific extension to the DOM API that renders the node and its descendants are essentially useless. Otherwise, Python’s garbage collector will eventually take care of the objects in the tree.
另请参阅
xml.dom.minidom
.
The definition of the DOM API for Python is given as part of the
xml.dom
module documentation. This section lists the differences between the API and
xml.dom.minidom
.
Node.
unlink
(
)
¶
Break internal references within the DOM so that it will be garbage collected on versions of Python without cyclic GC. Even when cyclic GC is available, using this can make large amounts of memory available sooner, so calling this on DOM objects as soon as they are no longer needed is good practice. This only needs to be called on the
Document
object, but may be called on child nodes to discard children of that node.
You can avoid calling this method explicitly by using the
with
statement. The following code will automatically unlink
dom
when the
with
block is exited:
with xml.dom.minidom.parse(datasource) as dom:
... # Work with dom.
Node.
writexml
(
writer
,
indent=""
,
addindent=""
,
newl=""
)
¶
Write XML to the writer object. The writer should have a
write()
method which matches that of the file object interface. The
indent
parameter is the indentation of the current node. The
addindent
parameter is the incremental indentation to use for subnodes of the current one. The
newl
parameter specifies the string to use to terminate newlines.
对于
Document
node, an additional keyword argument
encoding
can be used to specify the encoding field of the XML header.
Node.
toxml
(
encoding=None
)
¶
Return a string or byte string containing the XML represented by the DOM node.
With an explicit encoding [1] argument, the result is a byte string in the specified encoding. With no encoding argument, the result is a Unicode string, and the XML declaration in the resulting string does not specify an encoding. Encoding this string in an encoding other than UTF-8 is likely incorrect, since UTF-8 is the default encoding of XML.
Node.
toprettyxml
(
indent="\t"
,
newl="\n"
,
encoding=None
)
¶
Return a pretty-printed version of the document.
indent
specifies the indentation string and defaults to a tabulator;
newl
specifies the string emitted at the end of each line and defaults to
\n
.
encoding
argument behaves like the corresponding argument of
toxml()
.
This example program is a fairly realistic example of a simple program. In this particular case, we do not take much advantage of the flexibility of the DOM.
import xml.dom.minidom
document = """\
<slideshow>
<title>Demo slideshow</title>
<slide><title>Slide title</title>
<point>This is a demo</point>
<point>Of a program for processing slides</point>
</slide>
<slide><title>Another demo slide</title>
<point>It is important</point>
<point>To have more than</point>
<point>one slide</point>
</slide>
</slideshow>
"""
dom = xml.dom.minidom.parseString(document)
def getText(nodelist):
rc = []
for node in nodelist:
if node.nodeType == node.TEXT_NODE:
rc.append(node.data)
return ''.join(rc)
def handleSlideshow(slideshow):
print("<html>")
handleSlideshowTitle(slideshow.getElementsByTagName("title")[0])
slides = slideshow.getElementsByTagName("slide")
handleToc(slides)
handleSlides(slides)
print("</html>")
def handleSlides(slides):
for slide in slides:
handleSlide(slide)
def handleSlide(slide):
handleSlideTitle(slide.getElementsByTagName("title")[0])
handlePoints(slide.getElementsByTagName("point"))
def handleSlideshowTitle(title):
print("<title>%s</title>" % getText(title.childNodes))
def handleSlideTitle(title):
print("<h2>%s</h2>" % getText(title.childNodes))
def handlePoints(points):
print("<ul>")
for point in points:
handlePoint(point)
print("</ul>")
def handlePoint(point):
print("<li>%s</li>" % getText(point.childNodes))
def handleToc(slides):
for slide in slides:
title = slide.getElementsByTagName("title")[0]
print("<p>%s</p>" % getText(title.childNodes))
handleSlideshow(dom)
xml.dom.minidom
module is essentially a DOM 1.0-compatible DOM with some DOM 2 features (primarily namespace features).
Usage of the DOM interface in Python is straight-forward. The following mapping rules apply:
Document
object. Derived interfaces support all operations (and attributes) from the base interfaces, plus any new operations.
in
parameters, the arguments are passed in normal order (from left to right). There are no optional arguments.
void
operations return
None
.
foo
can also be accessed through accessor methods
_get_foo()
and
_set_foo()
.
readonly
attributes must not be changed; this is not enforced at runtime.
short
int
,
unsigned
int
,
unsigned
long
long
，和
boolean
all map to Python integer objects.
DOMString
maps to Python strings.
xml.dom.minidom
supports either bytes or strings, but will normally produce strings. Values of type
DOMString
may also be
None
where allowed to have the IDL
null
value by the DOM specification from the W3C.
const
declarations map to variables in their respective scope (e.g.
xml.dom.minidom.Node.PROCESSING_INSTRUCTION_NODE
); they must not be changed.
DOMException
is currently not supported in
xml.dom.minidom
. Instead,
xml.dom.minidom
uses standard Python exceptions such as
TypeError
and
AttributeError
.
NodeList
objects are implemented using Python’s built-in list type. These objects provide the interface defined in the DOM specification, but with earlier versions of Python they do not support the official API. They are, however, much more “Pythonic” than the interface defined in the W3C recommendations.
The following interfaces have no implementation in
xml.dom.minidom
:
DOMTimeStamp
DocumentType
DOMImplementation
CharacterData
CDATASection
Notation
Entity
EntityReference
DocumentFragment
Most of these reflect information in the XML document that is not of general utility to most DOM users.
脚注
| [1] | The encoding name included in the XML output should conform to the appropriate standards. For example, “UTF-8” is valid, but “UTF8” is not valid in an XML document’s declaration, even though Python accepts it as an encoding name. See https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl and https://www.iana.org/assignments/character-sets/character-sets.xhtml . |