>>> _isint("123")
    True
    >>> _isint("123.45")
    False

def _isint(string):
    """
    >>> _isint("123")
    True
    >>> _isint("123.45")
    False
    """
    return type(string) is int or \
           (isinstance(string, _binary_type) or isinstance(string, _text_type)) and \
           _isconvertible(int, string)