I am making a Django Web app which initalizes two large dictionaries when I load the home page. I would like this dictionary to be available to all views after being initialized first. I understand this could be done with Global variables. But how do this in Django without using Global Variable?
def startLoading():
p, songs = loadSongs()
I would like p and songs to be accessible and mutable from every view.
Django does not provide any way, per se, of doing that. Using global variables is, most of the times, a bad idea. My suggestion comes in the following steps:
Remember that, in Python, either you store something in a member of a global reference, or declare a global variable. This is a minor adjustment of what you did:
def startLoading():
global p, songs
# If you don't acquire a mutex here, God will flood earth again
if not (p or songs):
p, songs = loadSongs()
# release the mutex
return p, songs
I always suggest having another reference to store everything (the singleton I told you later):
from a.certain.module import my_store
def startLoading():
# ACQUIRE MUTEX here
if not myStore.has_data():
my_store.set_data(loadSongs())
# RELEASE MUTEX here
return my_store.get_data()
What get_data, set_data, and has_data do is up to you. I still think storing global values is a terrible idea in particular if you use something like gunicorn and have several (2n+1) django processes attending clients. It is always preferrable an external process like memcache to achieve that. But if you insist, you have these guidelines.
The most obvious way of doing this is to use Django Cache framework. You will need to add CACHES variable to your settings.py and then you can do something like this on project load
from django.conf import settings from django.core.cache import caches cache = caches['default'] key=settings.THEKEY # the cache key to access your dictionary the_dict = generate_the_big_dict() cache.set(key, the_dict)
and in your views that need to access the dictionary you would do something like
from django.conf import settings from django.core.cache import caches cache = caches['default'] key=settings.THEKEY the_dict = cache.get(key)
If you really only want to generate the key once, you can put the generation of it into the django app ready() method (relevant docs link https://docs.djangoproject.com/en/1.9/ref/applications/#django.apps.AppConfig.ready) and set some very large timeout value on it. Otherwise you might want to make sure somehow that you keep updating it before it expires.
