code: def HashBuffer(self, buf):
      
      for hasher in itervalues(self._hashers):
        hasher.update(buf)
        if self._progress:
          self._progress()
  
      self._bytes_read += len(buf)
docs: Updates underlying hashers with a given buffer.
  
      Args:
        buf: A byte buffer (string object) that is going to be fed to the hashers.