Get Mimetype for valid Image on Receiving Email via Google App Engine

How can I get the mimetype from an attachment when I receive a email via Google App Engine?

class ReceiveEmail开发者_开发技巧(InboundMailHandler):
    def receive(self,message):        
        sender = parseaddr(message.sender)[1]
        receiver = parseaddr(message.to)[1]

        # Attachments
        try:
            if message.attachments :
                # Attachments Image                    
                for a in message.attachments:

                    t = a[0].split('.')
                    t = t[len(t)-1].lower()

                    if t == 'png' or t == 'jpg' or t == 'jpeg' or t == 'gif':
                        logging.info('Image is correct')
                    else:
                        logging.info('Image is wrong')
        except: 
           # nothing

I have to know if the attached file in email is really an image? If I don't check this the user can upload an text.xml file which is only renamed to text.jpg.

How can I solve this problem?

I'm sorry, but I'm not sure if I have fully undestood the question.

You can use the built-in module mimetypes to identify the Mimetype. But the functions on this module will search for mimetypes on the file name only, so the user will be able to upload a text.xml renamed to text.jpg and be interpreted as a image.

If you are working with images only, maybe you can try to open the file as a PIL object to identify if it is a valid file, and work with the exception if it fails.

message is an instance of InboundEmailMessage, which has a method 'bodies'. bodies returns a list of (content_type, payload) tuples, so you can iterate over all the bodies like this:

for content_type, payload in message.bodies():
  # Do something with each part of the message

Alternately, you can pass a mimetype to message.bodies, which will return only parts with that mimetype.

You can also determine the mimetype from the filename, or using the mimetypes module as Nemeth suggests.