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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sizes(self):
 """ This method returns all the available sizes that can be used to create a droplet. """

        json = self.request('/sizes', method='GET')
        status = json.get('status')
        if status == 'OK':
            sizes_json = json.get('sizes', [])
            sizes = [Size.from_json(s) for s in sizes_json]
            return sizes
        else:
            message = json.get('message')
            raise DOPException('[%s]: %s' % (status, message))