docs: def len(self):
          """Length of the data stream"""
          # The len property is needed for requests.
          # requests checks __len__, then len
          # Since we cannot implement __len__ because python 32-bit uses 32-bit
          # sizes, we implement this instead.
          def stream_len(stream):
              """Stream length"""
              cur = stream.tell()
              try:
                  stream.seek(0, 2)
                  return stream.tell() - cur
              finally:
                  stream.seek(cur)
  
          return sum(stream_len(s) for s in self.streams)