Python中实现参数类型检查的简单方法

''' >>> NONE, MEDIUM, STRONG = 0, 1, 2 >>> >>> @accepts(int, int, int) ... def average(x, y, z): ...   return (x + y + z) / 2 ... >>> average(5.5, 10, 15.0) TypeWarning: 'average' method accepts (int, int, int), but was given (float, int, float) 15.25'''def accepts(*types, **kw):  """ Function decorator. Checks that inputs given to decorated function  are of the expected type.  Parameters:  types -- The expected types of the inputs to the decorated function.       Must specify type for each parameter.  kw  -- Optional specification of 'debug' level (this is the only valid       keyword argument, no other should be given).       debug = ( 0 | 1 | 2 )  """  if not kw:    # default level: MEDIUM    debug = 1  else:    debug = kw['debug']  try:    def decorator(f):      def newf(*args):        if debug == 0:          return f(*args)        assert len(args) == len(types)        argtypes = tuple(map(type, args))        if argtypes != types:          msg = info(f.__name__, types, argtypes, 0)          if debug == 1:            print >> sys.stderr, 'TypeWarning: ', msg          elif debug == 2:            raise TypeError, msg        return f(*args)      newf.__name__ = f.__name__      return newf    return decorator  except KeyError, key:    raise KeyError, key + "is not a valid keyword argument"  except TypeError, msg:    raise TypeError, msgdef info(fname, expected, actual, flag):  """ Convenience function returns nicely formatted error/warning msg. """  format = lambda types: ', '.join([str(t).split("'")[1] for t in types])  expected, actual = format(expected), format(actual)  msg = "'%s' method " % fname /     + ("accepts", "returns")[flag] + " (%s), but " % expected/     + ("was given", "result is")[flag] + " (%s)" % actual  return msg