code: def _slug_strip(self, value):
          
          re_sep = '(?:-|%s)' % re.escape(self.separator)
          value = re.sub('%s+' % re_sep, self.separator, value)
          return re.sub(r'^%s+|%s+$' % (re_sep, re_sep), '', value)
docs: Clean up a slug by removing slug separator characters that occur at
          the beginning or end of a slug.
  
          If an alternate separator is used, it will also replace any instances
          of the default '-' separator with the new separator.