def __expr(self):
        from compiler.ast import Discard, CallFunc, Name
        t = self.__tokenText()
        try:
            n= Discard(CallFunc(Name('__swrite__'), [self._cparse(t,'eval').getChildren()[0]],None,None))
            t = self.__tokenPop()
            _renumber(n,t[1]+1)
            return n
        except:
            self.__error('bad expression')
dataset/ETHPy150Open CGATOxford/cgat/obsolete/preppy.py/PreppyParser.__expr/operator `-` -> `+`