gistfile1.py

class FileSender(object):

    ...
    
    def send_data(self):
        chunk_size = 128 * 1024
    
        data = self.source.read(chunk_size)
    
        while data:
            self.checksum.update(data)
            yield self.client.send_data_chunk(data)
            data = self.source.read(chunk_size)

    def transfer(self):
        deferreds = []
    
        coop = task.Cooperator()
        work = self.send_data()
  
        return coop.coiterate(work)
    
    ...