I would like to be able to efficiently parse large HTML documents in Python. I am aware of Liza Daly's fastiter and the similar concept in the Python's own cElementTree. However, neither of these handle broken XML, which HTML reads as, well. In addition, the document may contain other broken XML.
Similarly, I'm aware of answers like this, which suggest not using any form of iterparse at all, and this is, in fact, what I'm using. However, I am trying to optimize past the biggest bottleneck in my program, which is the parsing of the documents.
Furthermore, I've done a little bit of experimentation using the SAX-style target handler for lxml parsers- I'm not sure what's going on, but it outright causes Python to stop working! Not merely throwing an exception, but a "python.exe has stopped working" message popup. I've no idea what's happening here, but I'm not even sure if this method is actually better than the standard parser, because I've seen very little about it on the Internet.
As such, my question is: Is there anything similar to iterparse, allowing me to quickly and efficiently parse through a document, that doesn't throw a snit fit when the document isn't well formed XML (IE. has recovery from poorly formed XML)?
I would use this one.
https://github.com/iogf/ehp
It is faster than lxml and it handles broken html like.
from ehp import *
doc = '''<html>
<body>
<p> cool </html></body>'''
html = Html()
dom = html.feed(doc)
print dom
It builds an AST according to the most possible HTML structure possible.
Then you can work on the AST.
I'm fairly new to Python, and I've just started working with XML parsing. I am getting a bit overwhelmed by all the options for working with XML, and I'm hoping an experienced person can give me some advice (and perhaps a code sample??) for the simple problem I'm working on.
I am working on a simple Python contact management application that does not involve a database - each contact's information is stored in a separate text file using XML. For example, assume the following is the contents of the file "1234.xml"
<contact>
<id>1234</id>
<name>Johnny Appleseed</name>
<phone>8145551212</phone>
<address>
<street>1234 Main Street</street>
<city>Hometown</city>
<state>OH</state>
</address>
<address>
<street>1313 Mockingbird Lane</street>
<city>White Plains</city>
<state>NY</state>
</address>
</contact>
For sake of example, let's assume there can be only one phone number, but multiple address blocks.
For what I'm doing here, I need to be able to parse the XML from the file, make changes to the data, and then update the XML and save it back to the file. Let's assume there are three types of data changes that might occur:
changing the data for one or more items, such as updating a phone number
adding a new address block (and the corresponding data for the street/city/state of the new address)
deleting an existing address block
Given what I'm trying to do here, can you recommend a particular way of doing this? (SAX, DOM, minidom, ElementTree, something else?) Code samples for whatever you suggest would be greatly appreciated.
Thank you!
Ron
The SAX and DOM APIs are older; they were pretty much translated from the Java world into Python. The ElementTree API was designed specifically to be Pythonic, i.e. to fit with the Python way of problem solving, so prefer that.
The richest and fastest implementation of ElementTree that I know of is lxml. It's XPath functionality is very useful. Untested example:
from lxml import etree
contacts = etree.parse(open("1234.xml"))
for c in contacts.xpath('//contact'):
if c.xpath('/name')[0].text == 'Johnny Appleseed':
c.xpath('/phone')[0].text = NEW_PHONE_NUMBER
print >> open("1234.xml", "w"), etree.tostring(contacts)
The best solution is to use ElementTree and parse this into a set of classes and manipulate the classes and then serialize them back to XML. You can do this by hand if the XML is really as simple as your example or you can use some tool or library to generate the bindings.
Working directly with XML in most cases always ends in tears, or at least hair pulling. It also isn't very maintainable, when the XML changes it usually will break your hand coded parsing.
Using a binding solution will be more robust to changes and easier to modify when you do need to manually intervene.
I am looking to write a program that searches for the tags in an xml document and changes the string between the tags from localhost to manager. The tag might appear in the xml document multiple times, and the document does have a definite path. Would python or vbscript make the most sense for this problem? And can anyone provide a template so I can get started? That would be great. Thanks.
If it's a simple thing, like changing a few strings here and there, you might be able to do everything with a python regexp, check here:
http://docs.python.org/library/re.html
For everything more complex, I would suggest using something like Beautiful Soup:
http://www.crummy.com/software/BeautifulSoup/documentation.html
It's a bit outdated, but contains everything you would ever need...
I agree this belongs to stackoverflow.com, as it's a programming question.
I suggest that you go straight to lxml library for python and don't look back. The regex manipulation of xml can have terrible consequences, and BeautifulSoup, although quite popular, is officially abandoned.
lxml is quite powerfull, fast and efficient. For your task, it is sufficient to write:
from lxml import etree
doc = etree.fromstring(content)
elements = doc.findall('tags_to_modify')
for el in elements:
el.text = your_replacement_function(el.text)
print etree.tostring(doc)
You can find a lot of help in lxml's documentation:
http://lxml.de/
I'm trying to decode a WBXML encoded SyncML message from a Nokia N95.
My first attempt was to use the python pywbxml module which wraps calls to libwbxml. Decoding the message with this gave a lot of <unknown> tags and a big chunk of binary within a <Collection> tag. I tried running the contents of the <Collection> through by itself but it failed. Is there something I'm missing?
Also, does anyone know of a pure python implementation of a wbxml parser? Failing that a command line or online tool to decode these messages would be useful -- it would make it a lot easier for me to write my own...
Funnily enough I've been working on the same problem. I'm about halfway through writing my own pure-Python WBXML parser, but it's not yet complete enough to be useful, and I have very little time to work on it right now.
Those <Unknown> tags might be because pywbxml / libwbxml doesn't have the right tag vocabulary loaded. WBXML represents tags by an index number to avoid transmitting the same tag name hundreds of times, and the table that maps index numbers to tag names has to be supplied separately from the WBXML document itself. From a vague glance at the libwbxml source it seems like libwbxml has a bunch of tag tables hard coded. It has tables for SyncML 1.0-1.2; I think my Nokia E71 sends SyncML 1.3 (if so, your N95 probably does too), which it looks like libwbxml doesn't support yet.
Getting it to work might be as simple as adding a SyncML 1.3 table to libwbxml. That said, last time I tried, pywbxml doesn't compile against the vanilla libwbxml source, so you have to apply some patches first... so "simple" may be a relative term.
I ended up writing a python parser myself. I managed to do it by following the spec here:
http://www.w3.org/TR/wbxml/
And then taking the code tables from the horde.org cvs.
The open mobile alliance's site and documentation are terrible, this was a very trying project :(
I used pywbxml ,
Just needed one patch in pywbxml.pyx:
params.lang in function wbxml2xml around line 25 set to:
params.lang = WBXML_LANG_UNKNOWN
works like charm. Also changing base class for WBXMLParseError to exception helps:
class WBXMLParseError(Exception):
I am about to build a piece of a project that will need to construct and post an XML document to a web service and I'd like to do it in Python, as a means to expand my skills in it.
Unfortunately, whilst I know the XML model fairly well in .NET, I'm uncertain what the pros and cons are of the XML models in Python.
Anyone have experience doing XML processing in Python? Where would you suggest I start? The XML files I'll be building will be fairly simple.
Personally, I've played with several of the built-in options on an XML-heavy project and have settled on pulldom as the best choice for less complex documents.
Especially for small simple stuff, I like the event-driven theory of parsing rather than setting up a whole slew of callbacks for a relatively simple structure. Here is a good quick discussion of how to use the API.
What I like: you can handle the parsing in a for loop rather than using callbacks. You also delay full parsing (the "pull" part) and only get additional detail when you call expandNode(). This satisfies my general requirement for "responsible" efficiency without sacrificing ease of use and simplicity.
ElementTree has a nice pythony API. I think it's even shipped as part of python 2.5
It's in pure python and as I say, pretty nice, but if you wind up needing more performance, then lxml exposes the same API and uses libxml2 under the hood. You can theoretically just swap it in when you discover you need it.
There are 3 major ways of dealing with XML, in general: dom, sax, and xpath. The dom model is good if you can afford to load your entire xml file into memory at once, and you don't mind dealing with data structures, and you are looking at much/most of the model. The sax model is great if you only care about a few tags, and/or you are dealing with big files and can process them sequentially. The xpath model is a little bit of each -- you can pick and choose paths to the data elements you need, but it requires more libraries to use.
If you want straightforward and packaged with Python, minidom is your answer, but it's pretty lame, and the documentation is "here's docs on dom, go figure it out". It's really annoying.
Personally, I like cElementTree, which is a faster (c-based) implementation of ElementTree, which is a dom-like model.
I've used sax systems, and in many ways they're more "pythonic" in their feel, but I usually end up creating state-based systems to handle them, and that way lies madness (and bugs).
I say go with minidom if you like research, or ElementTree if you want good code that works well.
I've used ElementTree for several projects and recommend it.
It's pythonic, comes 'in the box' with Python 2.5, including the c version cElementTree (xml.etree.cElementTree) which is 20 times faster than the pure Python version, and is very easy to use.
lxml has some perfomance advantages, but they are uneven and you should check the benchmarks first for your use case.
As I understand it, ElementTree code can easily be ported to lxml.
It depends a bit on how complicated the document needs to be.
I've used minidom a lot for writing XML, but that's usually been just reading documents, making some simple transformations, and writing them back out. That worked well enough until I needed the ability to order element attributes (to satisfy an ancient application that doesn't parse XML properly). At that point I gave up and wrote the XML myself.
If you're only working on simple documents, then doing it yourself can be quicker and simpler than learning a framework. If you can conceivably write the XML by hand, then you can probably code it by hand as well (just remember to properly escape special characters, and use str.encode(codec, errors="xmlcharrefreplace")). Apart from these snafus, XML is regular enough that you don't need a special library to write it. If the document is too complicated to write by hand, then you should probably look into one of the frameworks already mentioned. At no point should you need to write a general XML writer.
You can also try untangle to parse simple XML documents.
Since you mentioned that you'll be building "fairly simple" XML, the minidom module (part of the Python Standard Library) will likely suit your needs. If you have any experience with the DOM representation of XML, you should find the API quite straight forward.
I write a SOAP server that receives XML requests and creates XML responses. (Unfortunately, it's not my project, so it's closed source, but that's another problem).
It turned out for me that creating (SOAP) XML documents is fairly simple if you have a data structure that "fits" the schema.
I keep the envelope since the response envelope is (almost) the same as the request envelope. Then, since my data structure is a (possibly nested) dictionary, I create a string that turns this dictionary into <key>value</key> items.
This is a task that recursion makes simple, and I end up with the right structure. This is all done in python code and is currently fast enough for production use.
You can also (relatively) easily build lists as well, although depending upon your client, you may hit problems unless you give length hints.
For me, this was much simpler, since a dictionary is a much easier way of working than some custom class. For the books, generating XML is much easier than parsing!
For serious work with XML in Python use lxml
Python comes with ElementTree built-in library, but lxml extends it in terms of speed and functionality (schema validation, sax parsing, XPath, various sorts of iterators and many other features).
You have to install it, but in many places, it is already assumed to be part of standard equipment (e.g. Google AppEngine does not allow C-based Python packages, but makes an exception for lxml, pyyaml, and few others).
Building XML documents with E-factory (from lxml)
Your question is about building XML document.
With lxml there are many methods and it took me a while to find the one, which seems to be easy to use and also easy to read.
Sample code from lxml doc on using E-factory (slightly simplified):
The E-factory provides a simple and compact syntax for generating XML and HTML:
>>> from lxml.builder import E
>>> html = page = (
... E.html( # create an Element called "html"
... E.head(
... E.title("This is a sample document")
... ),
... E.body(
... E.h1("Hello!"),
... E.p("This is a paragraph with ", E.b("bold"), " text in it!"),
... E.p("This is another paragraph, with a", "\n ",
... E.a("link", href="http://www.python.org"), "."),
... E.p("Here are some reserved characters: <spam&egg>."),
... )
... )
... )
>>> print(etree.tostring(page, pretty_print=True))
<html>
<head>
<title>This is a sample document</title>
</head>
<body>
<h1>Hello!</h1>
<p>This is a paragraph with <b>bold</b> text in it!</p>
<p>This is another paragraph, with a
link.</p>
<p>Here are some reserved characters: <spam&egg>.</p>
</body>
</html>
I appreciate on E-factory it following things
Code reads almost as the resulting XML document
Readability counts.
Allows creation of any XML content
Supports stuff like:
use of namespaces
starting and ending text nodes within one element
functions formatting attribute content (see func CLASS in full lxml sample)
Allows very readable constructs with lists
e.g.:
from lxml import etree
from lxml.builder import E
lst = ["alfa", "beta", "gama"]
xml = E.root(*[E.record(itm) for itm in lst])
etree.tostring(xml, pretty_print=True)
resulting in:
<root>
<record>alfa</record>
<record>beta</record>
<record>gama</record>
</root>
Conclusions
I highly recommend reading lxml tutorial - it is very well written and will give you many more reasons to use this powerful library.
The only disadvantage of lxml is, that it must be compiled. See SO answer for more tips how to install lxml from wheel format package within a fraction of a second.
I strongly recommend SAX - Simple API for XML - implementation in the Python libraries. They are fairly easy to setup and process large XML by even driven API, as discussed by previous posters here, and have low memory footprint unlike validating DOM style XML parsers.
If you're going to be building SOAP messages, check out soaplib. It uses ElementTree under the hood, but it provides a much cleaner interface for serializing and deserializing messages.
I assume that the .NET way of processing XML builds on some version of MSXML and in that case I assume that using, for example, minidom would make you feel somewhat at home. However, if it is simple processing you are doing, any library will probably do.
I also prefer working with ElementTree when dealing with XML in Python because it is a very neat library.