QueryScheduler with two modes

import time


class QueryScheduler:
    NORMAL = 'normal'
    LIVE = 'live'

    def __init__(self, queries_normal, queries_live):
        self.mode = self.NORMAL
        self.queries_normal = queries_normal
        self.queries_live = queries_live
        self.waiting = self._in_waiting()

    def __iter__(self):
        return self

    def __next__(self):
        time.sleep(0.1)
        current_queries = [query for (query, freq, after) in self.waiting if time.time() > after]
        self.waiting = [
            (
                query,
                freq,
                time.time() + freq if time.time() > after else after,
            )
            for query, freq, after in self.waiting
        ]
        return current_queries

    def _in_waiting(self):
        if self.mode == self.NORMAL:
            queries = self.queries_normal
        elif self.mode == self.LIVE:
            queries = self.queries_live
        return [(query, freq, time.time() + freq) for query, freq in queries]

    def switch(self, mode):
        if self.mode == mode:
            return
        self.mode = mode
        self.waiting = self._in_waiting()


qs = QueryScheduler(
    [
        ('A', 10),
        ('B', 10),
        ('C', 10),
        ('D', 10),
    ],
    [
        ('A', 1),
        ('B', 5),
        ('C', 10),
        ('D', 15),
    ]
)

qs.switch(QueryScheduler.NORMAL)
for q in qs:
    if not q:
        continue
    print(q)
    # mode switch to LIVE
    if qs.mode == QueryScheduler.NORMAL:
        qs.switch(QueryScheduler.LIVE)