=====================
      Sending Binary Data
     =====================
     
     Sockets transmit streams of bytes.  Those bytes can contain text
     messages, as in the previous examples, or they can be made up of
     binary data that has been encoded for transmission.  To prepare binary
     data values for transmission, pack them into a buffer with
     :mod:`struct`.
     
     This client program encodes an integer, a string of two characters,
     and a floating point value into a sequence of bytes that can be passed
     to the socket for transmission.
     
     .. include:: socket_binary_client.py
        :literal:
        :start-after: #end_pymotw_header
     
     The server program uses the same :class:`Struct` specifier to unpack
     the bytes it receives.
     
     .. include:: socket_binary_server.py
        :literal:
        :start-after: #end_pymotw_header
     
     Running the client produces:
     
     ::
     
         $ python ./socket_binary_client.py 
         
         sending "0100000061620000cdcc2c40" (1, 'ab', 2.7)
         closing socket
     
     And the server shows the values it receives:
     
     ::
     
         $ python ./socket_binary_server.py 
         
         waiting for a connection
         received "0100000061620000cdcc2c40"
         unpacked: (1, 'ab', 2.700000047683716)
         
         waiting for a connection
     
     The floating point value loses some precision as it is packed and
     unpacked, but otherwise the data is transmitted as expected.  One
     thing to keep in mind is that depending on the value of the integer,
     it may be more efficient to convert it to text and then transmit,
     instead of using :mod:`struct`.  The integer ``1`` uses one byte when
     represented as a string, but four when packed into the structure.
     
     .. seealso::
     
         :mod:`struct`
             Converting between strings and other data types.