'Shift path segments from :attr:`path` to :attr:`script_name` and
vice versa.
:param shift: The number of path segments to shift. May be negative
to change the shift direction. (default: 1)'

def path_shift(self, shift=1):

    (script, path) = path_shift(self.environ.get('SCRIPT_NAME', '/'), self.path, shift)
    (self['SCRIPT_NAME'], self['PATH_INFO']) = (script, path)
