Tuesday, August 01, 2006

Agile investigation of the GDATA client with IronPython

Updated 13 May 2007 - Modified for new location and packaging of GData libraries.

This is the first coding entry in a series of posts about using IronPython to develop a GDATA reader. You will need to have IronPython RC1 or better installed, and either .NET 2.0 or Mono installed.

Download the Google GDATA client and unarchive the contents.

Find Google.GData.Client.dll and copy it to the directory you will using for this project.

One of the powerful things you gain from using a dynamic interpreted language for software development is the ability to discover, try and test ideas without the dreaded edit, compile, and debug cycle. To do this we change to the directory with gdata.dll and launch an IronPython interactive console.

ipy.exe -X:TabCompletion -X:ColorfulConsole -X:ExceptionDetail

If you are using Mono, the command is:

mono ipy.exe -X:TabCompletion -X:ColorfulConsole -X:ExceptionDetail

The -X switches are not required but I find they make my life a little easier.

Now we have a console running let's load the Google GDATA client assembly

IronPython 1.0.60725 on .NET 2.0.50727.42
Copyright (c) Microsoft Corporation. All rights reserved.
>>> import clr
>>> clr.AddReference("Google.GData.Client.dll")

To load a non-standard assembly, I need to tell IronPython about it. This is done by importing the the clr module and calling the AddReference method. Now that IronPython knows about the GDATA assembly, I can import from it the Python way. From the API docs, I know the namespace.

>>> import Google.GData.Client as GDClient

This loads the client class with an alias of GDClient so I can save some keystrokes. Now we can inspect the class using some Python introspection tools.

>>> dir(GDClient)
['AlternativeFormat', 'AtomBase', 'AtomBaseLink', 'AtomBaseLinkConverter', 'AtomCategory', 'AtomCategoryCollection', 'AtomContent', 'AtomContentConverter', 'AtomEntry', 'AtomEntryCollection', 'AtomEntryConverter', 'AtomFeed', 'AtomFeedParser', 'AtomGenerator', 'AtomGeneratorConverter', 'AtomIcon', 'AtomId', 'AtomLink', 'AtomLinkCollection', 'AtomLogo', 'AtomParserNameTable', 'AtomPerson', 'AtomPersonCollection', 'AtomPersonConverter', 'AtomPersonType', 'AtomSource', 'AtomSourceConverter', 'AtomTextConstruct', 'AtomTextConstructConverter', 'AtomTextConstructElementType', 'AtomTextConstructType', 'AtomUri', 'BaseFeedParser', 'BaseIsDirty', 'BaseIsPersistable', 'BaseMarkDirty', 'BaseNameTable', 'ClientFeedException', 'ClientQueryException', 'ExtensionElementEventArgs', 'ExtensionElementEventHandler', 'FeedParserEventArgs', 'FeedParserEventHandler', 'FeedQuery', 'GDataGAuthRequest', 'GDataGAuthRequestFactory', 'GDataLoggingRequest', 'GDataLoggingRequestFactory', 'GDataRequest', 'GDataRequestException', 'GDataRequestFactory', 'GDataRequestType', 'GoogleAuthentication', 'HttpFormPost', 'HttpMethods', 'IBaseWalkerAction', 'IExtensionElement', 'IGDataRequest', 'IGDataRequestFactory', 'IService', 'LoggedException', 'QueryCategory', 'QueryCategoryCollection', 'QueryCategoryOperator', 'RssFeedParser', 'Service', 'TokenCollection', 'Tracing', 'Utilities', '__builtins__', '__dict__', '__name__']

Based on my reading of the API docs, I am interested in the Service and FeedQuery classes.

>>> dir(GDClient.Service)
['Credentials', 'Delete', 'Equals', 'Finalize', 'GServiceAgent', 'GetHashCode', 'GetType', 'Insert', 'MakeDynamicType', 'MemberwiseClone', 'NewAtomEntry', 'NewExtensionElement', 'OnNewExtensionElement', 'OnParsedNewEntry', 'Query', 'QueryOpenSearchRssDescription', 'Reduce', 'ReferenceEquals', 'RequestFactory', 'StreamInsert', 'ToString', 'Update', '__class__', '__doc__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', 'add_NewAtomEntry', 'add_NewExtensionElement', 'remove_NewAtomEntry', 'remove_NewExtensionElement']
>>> GDClient.Service.__doc__
'Service()\nService(str applicationName)\nService(str service, str applicationName)\nService(str service, str applicationName, str library)'
'Get: Uri Uri(self)\nSet: Uri(self) = value\n'

Using dir we are able to see the methods and properties of the Google.GData.Client Service and FeedQuery classes have. Another nice feature is .NET classes imported under IronPython have an auto-generated __doc__ property that shows the overloaded constructors for the class.

Now we can try to read a GDATA feed. So we need a website with a feed that is Atom 1.0 compliant, for this example we will use http://feedparser.org/docs/examples/atom10.xml
>>> query = GDClient.FeedQuery()
>>> import System
>>> query.Uri = System.Uri("http://feedparser.org/docs/examples/atom10.xml")
>>> service = GDClient.Service("cl","hexdump-gdatareader-0.1")

Since the Uri property of FeedQuery requires a .NET Uri type, we must import the CLR System module.

Now we can read the GDATA feed and iterate over the returned entries.
>>> feed = service.Query(query)
>>> for entry in feed.Entries:
... print entry.Title.Text
First entry title

Based on this investigation of the GDATA client we can now create a simple python script to read a feed (Download).

import clr
import System
import Google.GData.Client as GDClient

def parse(uri, nc=None):
# Create a query and service object
query = GDClient.FeedQuery()
service = GDClient.Service("cl","hexdump-gdatareader-0.1")
query.Uri = System.Uri(uri)
return service.Query(query)

if __name__ == "__main__":
feed = parse("http://feedparser.org/docs/examples/atom10.xml")
for entry in feed.Entries:
print entry.Title.Text,":",entry.Summary.Text

Then run it from the commandline

ipy.exe gdatareader.py
First entry title:Watch out for nasty tricks

Hopefully this post has given you an insight in how IronPython can help with .NET/Mono software development. In the next post we will give the GDATA reader a GUI to make it more useful.


rezzrovv said...

the link to the next post about building a GUI has an extra "http://".

Mark Rees said...