# Django Celery

***

**1. Asynchronous Task Queuing**

```python
from celery import task

@task
def send_email(email_address, message):
    # Send an email to the given address with the provided message
    pass
```

**2. Scheduling Future Tasks**

```python
from celery.schedules import crontab
from celery.decorators import periodic_task

@periodic_task(run_every=crontab(hour='*', minute='0'))
def cleanup_old_data():
    # Remove old and unused data from the database
    pass
```

**3. Chaining Asynchronous Tasks**

```python
from celery import group

@task
def task1(arg1, arg2):
    return 'result from task1'

@task
def task2(arg1):
    return 'result from task2'

task = group(task1.s('arg1', 'arg2'), task2.s('result from task1'))
```

**4. Retrying Failed Tasks**

```python
from celery import task

@task
def unstable_task():
    # Do something that might fail
    pass
unstable_task.retry(countdown=60, max_retries=5)
```

**5. Using Celery Beat Scheduler**

```python
from celery.schedules import crontab
from celery.beat import Scheduler

scheduler = Scheduler(app='my_app')
scheduler.add(task='send_email', schedule=crontab(hour='*', minute='0'), args=('my_email@example.com', 'Hi there!'))
```

**6. Custom Task Retry Behavior**

```python
from celery.task import Task

class MyTask(Task):
    autoretry_for = (Exception,)
    max_retries = 5
    retry_backoff = True
    retry_backoff_max = 600
```

**7. Using the CeleryResult Class**

```python
from celery import Celery

celery = Celery('my_app')

@celery.task
def add(x, y):
    return x + y

result = add.delay(3, 4)
print(result.get())  # prints 7
```

**8. Tracking Task Progress**

```python
from celery.canvas import Signature

task = Signature('task.name').set(on_success=progress_handler, on_failure=failure_handler)
```

**9. Customizing Celery Broker**

```python
app = Celery('my_app', broker='amqp://guest:guest@localhost:5672')
```

**10. Overriding Default Task Parameters**

```python
from celery import Celery

app = Celery('my_app', task_default_queue='my_custom_queue')
```

**11. Using the Celery Event System**

```python
from celery.task import chord

@task
def subtask(i):
    return i * i

@task
def callback(results):
    print(sum(results))

chord(subtask.s(i) for i in range(10))(callback)
```

**12. Configuring Celery Workers**

```python
from celery import Celery

app = Celery('my_app', concurrency=4, max_tasks_per_child=100)
```

**13. Handling Task Timeouts**

```python
from celery.task import task

@task(time_limit=30)
def long_running_task():
    # Do something that might take longer than 30 seconds
    pass
```

**14. Customizing Task Serialization**

```python
from celery.utils import serialization
from celery.task import task

serialization.register_decoder('my_custom_coder', custom_decoder)

@task(serializer='my_custom_coder')
def my_task():
    pass
```

**15. Rate Limiting Tasks**

```python
from celery.task import task
from celery.utils.ratelimit import RateLimitExceeded

@task
def rate_limited_task():
    if RateLimitExceeded():
        raise RateLimitExceeded('Rate limit exceeded!')
    # Do something
    pass
```

**16. Prioritizing Tasks**

```python
from celery import task, priority

@task(priority=10)
def high_priority_task():
    pass
```

**17. Using Celery Groups**

```python
from celery import group

group(task1.s(), task2.s(), task3.s()).apply_async()
```

**18. Creating Custom Celery Events**

```python
from celery import signals

@signals.worker_ready.connect
def on_worker_ready(sender, **kwargs):
    print('Worker is ready!')
```

**19. Customized Task Retrying Policies**

```python
from celery.utils import retry

def my_retry(result, exc, tb):
    print('Retrying task...')
    return retry(exc, result)

@task(retry_policy=my_retry)
def my_task():
    pass
```

**20. Handling Async Result Callbacks**

```python
from celery.app.task import Task

class MyTask(Task):
    def after_return(self, status, retval, task_id, args, kwargs, einfo):
        print('Task has returned with status', status)
```

**21. Using Celery with Redis**

```python
app = Celery('my_app', broker='redis://localhost:6379')
```

**22. Configuring Task Routing**

```python
app = Celery('my_app')
app.conf.task_routes = {
    'tasks.add': 'worker1',
    'tasks.multiply': 'worker2',
}
```

**23. Customizing Celery Beat Scheduler**

```python
from celery.beat import ScheduleEntry
from datetime import timedelta

schedule = {
    'add-numbers': {
        'task': 'tasks.add',
        'schedule': timedelta(seconds=30),
    },
}

beat_scheduler = ScheduleEntry.from_dict(schedule)
```

**24. Using Django ORM with Celery**

```python
from django.db import transaction

@task
def update_user(user_id, new_data):
    with transaction.atomic():
        user = User.objects.get(pk=user_id)
        for key, value in new_data.items():
            setattr(user, key, value)
        user.save()
```

**25. Handling Task Execution Errors**

```python
from celery.exceptions import Ignore

@task(ignore_result=True)
def ignore_errors_task():
    # Do something that might raise an exception
    raise Exception()
```

**26. Using Celery with Docker**

```
docker-compose up -d
# build image
docker-compose build
# run tests
docker-compose run --rm web celery --app=my_app test
```

**27. Customizing Celery Worker Prefetch Multiplier**

```python
app = Celery('my_app', worker_prefetch_multiplier=1)
```

**28. Using Celery with MongoDB**

```python
app = Celery('my_app', broker='mongodb://localhost:27017/celery')
```

**29. Creating Custom Task Lock**

```python
from celery.locks import Lock

lock = Lock('my_task_lock')
with lock.acquire():
    # Do something protected by the lock
    pass
```

**30. Setting Up Celery with RabbitMQ**

```
rabbitmq-server
celery -A my_app worker --loglevel=info
```

**31. Using Celery with Flask**

```python
from flask import Flask
from celery import Celery

app = Flask(__name__)
celery = Celery(app.name, broker='redis://localhost:6379')
```

**32. Customizing Celery Worker Pool**

```python
from celery.worker import autoscale

autoscaler = autoscale.PeriodicWorkerScaler(
    min_concurrency=1,
    max_concurrency=5,
    keepalive=60,
    max_tasks_per_child=100,
)
```

**33. Sending Tasks from Django Views**

```python
from django.views import View
from celery.result import AsyncResult

class MyView(View):
    def post(self, request):
        task = my_task.delay(request.data)
        return JsonResponse(
            {'task_id': task.id},
            status=202
        )
```

**34. Using Celery with Flower UI**

```
celery flower
```

**35. Setting Up Celery with PostgreSQL**

```
psql -h localhost -U postgres -d postgres
CREATE DATABASE celery;
CREATE USER celery WITH PASSWORD 'my_password';
GRANT ALL PRIVILEGES ON DATABASE celery TO celery;
```

**36. Configuring Celery Beat Scheduler with Django**

```python
from django.conf import settings
from celery.schedules import crontab
from celery.beat import Scheduler

class MyScheduler(Scheduler):
    schedule = {
        'my-scheduled-task': {
            'task': 'my_app.tasks.my_task',
            'schedule': crontab(minute='0', hour='*'),
            'args': (),
        },
    }

    def setup_schedule(self):
        super().setup_schedule(settings.CELERYD_CHORD_PROPAGATION)
```