Python 3.x ModuleNotFoundError:没有名为'；apscheduler'；使用python3时

使用此命令启动项目时：

~/source/pydolphin on  master! ⌚ 15:52:02
$ python3.9 schedulespider.py                                                                          ‹ruby-2.7.2›
Traceback (most recent call last):
  File "/Users/dolphin/source/pydolphin/schedulespider.py", line 4, in <module>
    from apscheduler.schedulers.background import BackgroundScheduler
ModuleNotFoundError: No module named 'apscheduler'
(base)

但问题仍然存在，我应该怎么做才能解决它？这是我的Python代码：

# coding=utf-8

import time
from apscheduler.schedulers.background import BackgroundScheduler

from dolphin.biz.RssEntry import RssEntry

if __name__ == '__main__':
    scheduler = BackgroundScheduler()
    rss = RssEntry()
    scheduler.add_job(rss.rss_sub, 'cron', minute='*/1', max_instances=10)
    scheduler.start()
    try:
        while True:
            time.sleep(20)
    except (KeyboardInterrupt, SystemExit):
        scheduler.shutdown()

# coding=utf-8

import time
from apscheduler.schedulers.background import BackgroundScheduler

from dolphin.biz.RssEntry import RssEntry

if __name__ == '__main__':
    scheduler = BackgroundScheduler()
    rss = RssEntry()
    scheduler.add_job(rss.rss_sub, 'cron', minute='*/1', max_instances=10)
    scheduler.start()
    try:
        while True:
            time.sleep(20)
    except (KeyboardInterrupt, SystemExit):
        scheduler.shutdown()