def inc_value(self, key, count=1, start=0, spider=None):
        """Set increment of value according to key"""
        if not self.server.hexists(self._get_key(spider), key):
            self.set_value(key, start)
        self.server.hincrby(self._get_key(spider), key, count)
Set increment of value according to key
src/scrapy_redis/stats.py