Django snippets

#Author: Orcun Avsar < orc.avs@gmail.com >





import os
import sys
import time
import datetime
import imp




DIR=os.path.abspath(__file__)
os.environ['DJANGO_SETTINGS_MODULE'] = 'settings'

sys.path.append(os.path.split(os.path.split(DIR)[0])[0])
sys.path.append(imp.find_module("django")[1])


class ComponentError(Exception):
	def __init__(self,component,components):
		self.components=components
		self.component=component
	def __str__(self):
		return "Invalid component:"+self.component+". Available components: "+",".join(self.components)
		

class BaseCron:
    def __init__(self):
        self.events={}
	self.components=["year","month","day","hour","minute","second"]
    def add_event(self,event,period,component,round=False):
	if not self.components.count(component):
		raise ComponentError(component,self.components)
	self.events[event]={"period":period,"component":component,"round":round}
	self.find_next(event)
    def find_next(self,event):
	now=datetime.datetime.now()
	comps={"year":now.year,
		"month":now.month,
		"day":now.day,
		"hour":now.hour,
		"minute":now.minute,
		"second":now.second}
	component=self.events[event]["component"]
	period=self.events[event]["period"]
	if component=="year":
		comps[component]+=period
	elif component=="month":
		comps[component]=range(1, 13)[(comps[component]+period)%12]
		if comps[component]==1:comps["year"]+=1
	else:
		karg={component+"s":period}	
		time_delta=datetime.timedelta(**karg)
		next=now+time_delta
		comps={"year":next.year,
				"month":next.month,
				"day":next.day,
				"hour":next.hour,
				"minute":next.minute,
				"second":next.second}
	round=self.events[event]["round"]
    	extra_time_delta=None
	if round:
            for comp in self.components[(self.components.index(component))+1:]:
                value=1
                comps[comp]=value
            if component=="year":
                comps[component]+=1
            elif component=="month":
                comps[component]=(range(1, 13)[(comps[component]+1)%12])
                if comps[component]==1:comps["year"]+=1
            else:
                karg={component+"s":1}	
                extra_time_delta=datetime.timedelta(**karg)
	next_visit=datetime.datetime(**comps)
	if extra_time_delta:
		next_visit+=extra_time_delta
	self.events[event]["next_visit"]=next_visit
    def start(self):
        while 1:
            ###sorting job###
	    list=[(self.events[x]["next_visit"],x) for x in self.events.keys()]
	    list.sort()
	    event_name=list[0][1]
	    event_date=list[0][0]
	    now=datetime.datetime.now()
	    timedelta=event_date-now
	    seconds=(timedelta.days*24*60*60)+timedelta.seconds
	    print "\nnext job: '"+event_name +"' in "+str(seconds)+" seconds..."
	    if timedelta.days>=0:
		    time.sleep(seconds)
	    print "processing job..."
	    getattr(self,event_name)()
	    print "finished succesfully."
	    self.find_next(event_name)


"""

you can import your models here like:
from my_project.entry.models import Entry 


start your Cron class here. inherit from BaseCron above
class MyCron(BaseCron):
	def __init__(self):
                BaseCron.__init__(self)
		self.add_event("test_job",3,"minute",True)
	def test_job(self):
		Entry.objects.all()

create only one instance otherwise only one will work 
as cron runs in continuous loop

cron=MyCron()

and start it...

cron.start()

that's all you have to do .




####DETAILS#####

we added a test_job function which is going to run in every three minutes and
will be rounded minutely

add_event function adds  a new job to schedule.
        -first argument is function name
	-second is period length
	-third is period component ("second","minute","hour","day","month" or "year"
	-last one tells if time should be rounded to period component
	
e.g. you want to add a job that will run on every day at 24.00 .  your add_event function shuld be like that:
	self.add_event("midnight_function",1,"day",True)

"""