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How to Handle Incoming Attachments on Google App Engine

I just finished writing an app on Google App Engine in Python that receives incoming email that may or may not have an attachment and came across a little quirk that I want to share.

According to the App Engine documentation, when receiving email, the attachments attribute will have a value of tuples for each attachment, or it may be empty.
So according to that documentation I iterated the attachments attribute for all incoming emails. Turns out, when using the SDK development server for testing, I was getting this error:

AttributeError: 'InboundEmailMessage' object has no attribute 'attachments'

My code was very simple, "for filename, filecontents in message.attachments:"

Well here is some code that works:

            # handle attachments
            if hasattr(message, 'attachments'):
                for filename, filecontents in message.attachments:
                    a = model.Attachment()
                    a.filename = filename
                    a.contents = filecontents.decode()
                    a.put()

And that solved my problem. I had to use the hasattr method to check to see if the attachments attribute existed.

The second problem is the documentation does not tell you to use the decode function. If you try to save the attachment into a blob in the datastore, it will tell you it is expecting a str object and error out if you do not use the .decode() method. So make sure you remember to use it as well as you're dealing with binary data here.

Enjoy your coding!