'Set the font stretch or width.  Options are: \'ultra-condensed\',
\'extra-condensed\', \'condensed\', \'semi-condensed\', \'normal\',
\'semi-expanded\', \'expanded\', \'extra-expanded\' or
\'ultra-expanded\', or a numeric value in the range 0-1000.'

def set_stretch(self, stretch):

    if (stretch is None):
        stretch = rcParams[u'font.stretch']
    try:
        stretch = int(stretch)
        if ((stretch < 0) or (stretch > 1000)):
            raise ValueError()
    except ValueError:
        if (stretch not in stretch_dict):
            raise ValueError(u'stretch    is    invalid')
    self._stretch = stretch
