Python 实用宝典

Question 1

I am creating a GUI frontend for the Eve Online API in Python.

I have successfully pulled the XML data from their server.

I am trying to grab the value from a node called “name”:

from xml.dom.minidom import parse
dom = parse("C:\\eve.xml")
name = dom.getElementsByTagName('name')
print name

This seems to find the node, but the output is below:

[<DOM Element: name at 0x11e6d28>]

How could I get it to print the value of the node?

Question 2

It should just be

name[0].firstChild.nodeValue

Question 3

Probably something like this if it’s the text part you want…

from xml.dom.minidom import parse
dom = parse("C:\\eve.xml")
name = dom.getElementsByTagName('name')

print " ".join(t.nodeValue for t in name[0].childNodes if t.nodeType == t.TEXT_NODE)

The text part of a node is considered a node in itself placed as a child-node of the one you asked for. Thus you will want to go through all its children and find all child nodes that are text nodes. A node can have several text nodes; eg.

<name>
  blabla
  <somestuff>asdf</somestuff>
  znylpx
</name>

You want both ‘blabla’ and ‘znylpx’; hence the ” “.join(). You might want to replace the space with a newline or so, or perhaps by nothing.

Question 4

you can use something like this.It worked out for me

doc = parse('C:\\eve.xml')
my_node_list = doc.getElementsByTagName("name")
my_n_node = my_node_list[0]
my_child = my_n_node.firstChild
my_text = my_child.data 
print my_text

Question 5

I know this question is pretty old now, but I thought you might have an easier time with ElementTree

from xml.etree import ElementTree as ET
import datetime

f = ET.XML(data)

for element in f:
    if element.tag == "currentTime":
        # Handle time data was pulled
        currentTime = datetime.datetime.strptime(element.text, "%Y-%m-%d %H:%M:%S")
    if element.tag == "cachedUntil":
        # Handle time until next allowed update
        cachedUntil = datetime.datetime.strptime(element.text, "%Y-%m-%d %H:%M:%S")
    if element.tag == "result":
        # Process list of skills
        pass

I know that’s not super specific, but I just discovered it, and so far it’s a lot easier to get my head around than the minidom (since so many nodes are essentially white space).

For instance, you have the tag name and the actual text together, just as you’d probably expect:

>>> element[0]
<Element currentTime at 40984d0>
>>> element[0].tag
'currentTime'
>>> element[0].text
'2010-04-12 02:45:45'e

Question 6

The above answer is correct, namely:

name[0].firstChild.nodeValue

However for me, like others, my value was further down the tree:

name[0].firstChild.firstChild.nodeValue

To find this I used the following:

def scandown( elements, indent ):
    for el in elements:
        print("   " * indent + "nodeName: " + str(el.nodeName) )
        print("   " * indent + "nodeValue: " + str(el.nodeValue) )
        print("   " * indent + "childNodes: " + str(el.childNodes) )
        scandown(el.childNodes, indent + 1)

scandown( doc.getElementsByTagName('text'), 0 )

Running this for my simple SVG file created with Inkscape this gave me:

nodeName: text
nodeValue: None
childNodes: [<DOM Element: tspan at 0x10392c6d0>]
   nodeName: tspan
   nodeValue: None
   childNodes: [<DOM Text node "'MY STRING'">]
      nodeName: #text
      nodeValue: MY STRING
      childNodes: ()
nodeName: text
nodeValue: None
childNodes: [<DOM Element: tspan at 0x10392c800>]
   nodeName: tspan
   nodeValue: None
   childNodes: [<DOM Text node "'MY WORDS'">]
      nodeName: #text
      nodeValue: MY WORDS
      childNodes: ()

I used xml.dom.minidom, the various fields are explained on this page, MiniDom Python.

Question 7

I had a similar case, what worked for me was:

name.firstChild.childNodes[0].data

XML is supposed to be simple and it really is and I don’t know why python’s minidom did it so complicated… but it’s how it’s made

Question 8

Here is a slightly modified answer of Henrik’s for multiple nodes (ie. when getElementsByTagName returns more than one instance)

images = xml.getElementsByTagName("imageUrl")
for i in images:
    print " ".join(t.nodeValue for t in i.childNodes if t.nodeType == t.TEXT_NODE)

Question 9

The question has been answered, my contribution consists in clarifying one thing that may confuse beginners:

Some of the suggested and correct answers used firstChild.data and others used firstChild.nodeValue instead. In case you are wondering what is the different between them, you should remember they do the same thing because nodeValue is just an alias for data.

The reference to my statement can be found as a comment on the source code of minidom:

#nodeValue is an alias for data

Question 10

It’s a tree, and there may be nested elements. Try:

def innerText(self, sep=''):
    t = ""
    for curNode in self.childNodes:
        if (curNode.nodeType == Node.TEXT_NODE):
            t += sep + curNode.nodeValue
        elif (curNode.nodeType == Node.ELEMENT_NODE):
            t += sep + curNode.innerText(sep=sep)
    return t

Question 11

What are the libraries that support XPath? Is there a full implementation? How is the library used? Where is its website?

Question 12

libxml2 has a number of advantages:

Compliance to the spec
Active development and a community participation
Speed. This is really a python wrapper around a C implementation.
Ubiquity. The libxml2 library is pervasive and thus well tested.

Downsides include:

Compliance to the spec. It’s strict. Things like default namespace handling are easier in other libraries.
Use of native code. This can be a pain depending on your how your application is distributed / deployed. RPMs are available that ease some of this pain.
Manual resource handling. Note in the sample below the calls to freeDoc() and xpathFreeContext(). This is not very Pythonic.

If you are doing simple path selection, stick with ElementTree ( which is included in Python 2.5 ). If you need full spec compliance or raw speed and can cope with the distribution of native code, go with libxml2.

Sample of libxml2 XPath Use

import libxml2

doc = libxml2.parseFile("tst.xml")
ctxt = doc.xpathNewContext()
res = ctxt.xpathEval("//*")
if len(res) != 2:
    print "xpath query: wrong node set size"
    sys.exit(1)
if res[0].name != "doc" or res[1].name != "foo":
    print "xpath query: wrong node set value"
    sys.exit(1)
doc.freeDoc()
ctxt.xpathFreeContext()

Sample of ElementTree XPath Use

from elementtree.ElementTree import ElementTree
mydoc = ElementTree(file='tst.xml')
for e in mydoc.findall('/foo/bar'):
    print e.get('title').text

Question 13

The lxml package supports xpath. It seems to work pretty well, although I’ve had some trouble with the self:: axis. There’s also Amara, but I haven’t used it personally.

Question 14

Sounds like an lxml advertisement in here. ;) ElementTree is included in the std library. Under 2.6 and below its xpath is pretty weak, but in 2.7+ much improved:

import xml.etree.ElementTree as ET
root = ET.parse(filename)
result = ''

for elem in root.findall('.//child/grandchild'):
    # How to make decisions based on attributes even in 2.6:
    if elem.attrib.get('name') == 'foo':
        result = elem.text
        break

Question 15

Use LXML. LXML uses the full power of libxml2 and libxslt, but wraps them in more “Pythonic” bindings than the Python bindings that are native to those libraries. As such, it gets the full XPath 1.0 implementation. Native ElemenTree supports a limited subset of XPath, although it may be good enough for your needs.

Question 16

Another option is py-dom-xpath, it works seamlessly with minidom and is pure Python so works on appengine.

import xpath
xpath.find('//item', doc)

Question 17

You can use:

PyXML:

from xml.dom.ext.reader import Sax2
from xml import xpath
doc = Sax2.FromXmlFile('foo.xml').documentElement
for url in xpath.Evaluate('//@Url', doc):
  print url.value

libxml2:

import libxml2
doc = libxml2.parseFile('foo.xml')
for url in doc.xpathEval('//@Url'):
  print url.content

Question 18

The latest version of elementtree supports XPath pretty well. Not being an XPath expert I can’t say for sure if the implementation is full but it has satisfied most of my needs when working in Python. I’ve also use lxml and PyXML and I find etree nice because it’s a standard module.

NOTE: I’ve since found lxml and for me it’s definitely the best XML lib out there for Python. It does XPath nicely as well (though again perhaps not a full implementation).

Question 19

You can use the simple soupparser from lxml

Example:

from lxml.html.soupparser import fromstring

tree = fromstring("<a>Find me!</a>")
print tree.xpath("//a/text()")

Question 20

If you want to have the power of XPATH combined with the ability to also use CSS at any point you can use parsel:

>>> from parsel import Selector
>>> sel = Selector(text=u"""<html>
        <body>
            <h1>Hello, Parsel!</h1>
            <ul>
                <li><a href="http://example.com">Link 1</a></li>
                <li><a href="http://scrapy.org">Link 2</a></li>
            </ul
        </body>
        </html>""")
>>>
>>> sel.css('h1::text').extract_first()
'Hello, Parsel!'
>>> sel.xpath('//h1/text()').extract_first()
'Hello, Parsel!'

Question 21

Another library is 4Suite: http://sourceforge.net/projects/foursuite/

I do not know how spec-compliant it is. But it has worked very well for my use. It looks abandoned.

Question 22

PyXML works well.

You didn’t say what platform you’re using, however if you’re on Ubuntu you can get it with sudo apt-get install python-xml. I’m sure other Linux distros have it as well.

If you’re on a Mac, xpath is already installed but not immediately accessible. You can set PY_USE_XMLPLUS in your environment or do it the Python way before you import xml.xpath:

if sys.platform.startswith('darwin'):
    os.environ['PY_USE_XMLPLUS'] = '1'

In the worst case you may have to build it yourself. This package is no longer maintained but still builds fine and works with modern 2.x Pythons. Basic docs are here.

Question 23

If you are going to need it for html:

import lxml.html as html
root  = html.fromstring(string)
root.xpath('//meta')

Python 实用宝典

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