multiple notifications from crontab in Django

I have a crontab in django/python, the code is given below. It is sending multiple notifications at the same time instead of sending single one. what is the problem?

`def send_statistics():
    today = date.today()
    yesterday = today - timedelta(days=1)
    try:
        if StatisticModel.objects.filter(date=yesterday).exists():
            stat = StatisticModel.objects.get(date=yesterday)
            if not stat.is_send:
                text = "some text"
                send_message_telegram(text, SEND_STATISTIC_GROUP_ID)
                stat.is_send = True
                stat.save()
                time.sleep(100)
        else:
            StatisticModel.objects.create(is_send=True, date=yesterday)
            text = f"<b>*******HISOBOT*******</b>\n" \
            send_message_telegram(text, SEND_STATISTIC_GROUP_ID)
            time.sleep(100)
    except:
        send_message_telegram
def start():
    scheduler = BackgroundScheduler({'apscheduler.timezone': 'Asia/Tashkent'})

    scheduler.add_job(send_statistics, 'cron', hour=9)
    scheduler.start()`

it's because, gunicorn workers are calling this cron job simultaneously. That's why it's sending multiple notifications.
As a solution, you may use caching.

from django.core.cache import cache

def send_statistics():
    # Try to acquire the lock
    if cache.add('statistics_lock', 'true', timeout=600):
        try:
            # The rest of your function here...
            ...
        finally:
            # Always make sure to release the lock when done
            cache.delete('statistics_lock')
    else:
        # If we couldn't acquire the lock, that means another instance is already running the task
        pass```


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