code: def _copy_chunk(src, dst, length):
      "Copy length bytes from file src to file dst."
      BUFSIZE = 128 * 1024
      while length > 0:
          l = min(BUFSIZE, length)
          buf = src.read(l)
          assert len(buf) == l
          dst.write(buf)
          length -= f _copy_chunk(src, dst, length):
      "Copy length bytes from file src to file dst."
      BUFSIZE = 128 * 1024
      while length > 0:
          l = min(BUFSIZE, length)
          buf = src.read(l)
          assert len(buf) == l
          dst.write(buf)
          length -= l
docs: Copy length bytes from file src to file dst.