code: def best_prefix(bytes, system=NIST):
      
      if isinstance(bytes, Bitmath):
          value = bytes.bytes
      else:
          value = bytes
      return Byte(value).best_prefix(system=system)
docs: Return a bitmath instance representing the best human-readable
  representation of the number of bytes given by ``bytes``. In addition
  to a numeric type, the ``bytes`` parameter may also be a bitmath type.
  
  Optionally select a preferred unit system by specifying the ``system``
  keyword. Choices for ``system`` are ``bitmath.NIST`` (default) and
  ``bitmath.SI``.
  
  Basically a shortcut for:
  
     >>> import bitmath
     >>> b = bitmath.Byte(12345)
     >>> best = b.best_prefix()
  
  Or:
  
     >>> import bitmath
     >>> best = (bitmath.KiB(12345) * 4201).best_prefix()