Handlers that execute right before and right after a task is executed in celery.

celery_before_after.py

from celery import Celery
from celery.signals import after_task_publish,task_success,task_prerun,task_postrun

# first argument, current module
app = Celery('tasks')
app.config_from_object('celeryconfig')

# To instantiate celery and import this module 
# do: celery -A task worker --loglevel=info
# after, once celery is running, instantiate a python console:
'''
from task import add
add.delay(4,4)
'''
# config:
'''
BROKER_URL                          = 'redis://localhost:6379/0'
CELERY_RESULT_BACKEND               = 'redis://localhost:6379/0'
CELERY_TASK_RESULT_EXPIRES          = 3600
CELERY_DISABLE_RATE_LIMITS          = True
CELERY_STORE_ERRORS_EVEN_IF_IGNORED = True
CELERYD_CONCURRENCY                 = 16
CELERYD_TASK_TIME_LIMIT             = 3630
CELERY_TIMEZONE = 'UTC'
CELERYBEAT_SCHEDULE = {
    'add-every-30-seconds': {
        'task': 'task.add',
        'schedule': timedelta(seconds=30),
        'args': (16, 16)
    },
}
'''

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

@app.task
def write(msg):
    # opening file for apending
    # this task does not return anything
    f = open('logfile','a');
    f.write(str(msg))
    f.close()

@app.task
def evil_add(x,y):
    raise Exception('Boom!')


#####################################
'''
another example of how to add the 'hooks'
class Celery(object):
    @staticmethod
    def install():
        task_prerun.connect(task_prerun)
        task_postrun.connect(task_postrun)
'''
#####################################


@task_prerun.connect()
def task_prerun(signal=None, sender=None, task_id=None, task=None, args=None, kwargs=None):
    if task.name =="task.add":
        print "pre-run of add. Do special add things here. Task: {0}  sender: {1}".format(task,sender)


@task_postrun.connect()
def task_postrun(signal=None, sender=None, task_id=None, task=None, args=None, kwargs=None, retval=None, state=None):
    # note that this hook runs even when there has been an exception thrown by the task
    print "post run {0} ".format(task)

thanks for the example.
this is not overwriting the names in celery.signals, but only in this source.