def add(self, **kwargs):
    for (key, val) in kwargs.items():
        if (key not in self.stats.keys()):
            self.stats[key] = list()
        self.stats[key].append(val)
def add(self, **kwargs):
    for (key, val) in kwargs.items():
        if (key not in self.stats.keys()):
            self.stats[key] = list()
        self.stats[key].append(val)