Validate a single value with type_check.

def _ValidateValue(value, type_check):
  """Validate a single value with type_check."""
  if inspect.isclass(type_check):
    return isinstance(value, type_check)
  if isinstance(type_check, tuple):
    return _ValidateTuple(value, type_check)
  elif callable(type_check):
    return type_check(value)
  else:
    raise TypeError("Invalid type check '%s'" % repr(type_check))