code: def compress(x, y):
      
      polarity = "02" if y % 2 == 0 else "03"
  
      wrap = lambda x: x
      if not is_py2:
          wrap = lambda x: bytes(x, 'ascii')
  
      return unhexlify(wrap("%s%0.64x" % (polarity, x)))
docs: Given a x,y coordinate, encode in "compressed format"
      Returned is always 33 bytes.