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Friday, July 06, 2012

Calling the Google Drive API and other Google APIs asynchronously with Twisted

You may know that the Google API Python Client is built on httplib2. This is a reasonable general choice, but the tight coupling is unhelpful in situations where a different HTTP library, or an entirely different approach to network programming should be used. An example of this is Twisted.

Aside: I won't be going on about how awesome Twisted is, but let's just take it for granted that it is so awesome that I could not write this application without it.

Httplib2 is blocking, and that makes it incompatible with being run inside the Twisted reactor. Fortunately we are only the latest person to have this problem, and a solution exists:


api_call = drive.files().list()

def on_list(resp):
  for item in resp['items']:
    print item['title']

d = deferToThread(api_call.execute)

A blocking call will be called in a thread and will callback on the returned deferred when it is done. I appreciate that no one* is 100% happy with this solution. "Argh, threads!", "Argh, async!" But it is a testament to the Greatness of Twisted that it has this sort of facility to play well with other, less flexible, systems.

*Did I mention? I am 100% happy.

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