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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 create_screenshot(self, app_id, filename, position=1):
 """Add a screenshot to the web app identified by by ``app_id``. Screenshots are ordered by ``position``. :returns: HttpResponse: * status_code (int) 201 is successful * content (dict) containing screenshot data """

        # prepare file for upload
        with open(filename, 'rb') as s_file:
            s_content = s_file.read()
        s_encoded = b64encode(s_content)
        url = self.url('create_screenshot') % app_id

        mtype, encoding = mimetypes.guess_type(filename)
        if mtype is None:
            mtype = 'image/jpeg'

        data = {'position': position,
                'file': {'type': mtype,
                         'data': s_encoded}}
        return self.conn.fetch('POST', url, data)