def prextend(self, var, values, create=False):
        if create:
            cur = self.get(var, [])
        else:
            cur = self[var]
        self[var] = values + cur
Prepend a list of values in front of self[var].
dataset/ETHPy150Open cournape/Bento/bento/private/_yaku/yaku/environment.py/Environment.prextend