django-stash

Remember a value for the rest of the current request, and read it back from anywhere — without passing request around.

import stash

def get_current_tenant():
    return stash.get_or_set("tenant", lambda: Tenant.objects.get(pk=...))

Call it ten times in one request: the loader runs once. Next request: it runs again.

This is not a cache backend. Nothing is shared between requests, processes, or workers. Values live only while a request is being handled, and are thrown away when it finishes.

Install

pip install django-stash

MIDDLEWARE = [
    "stash.middleware.StashMiddleware",
    # ...
]

No INSTALLED_APPS entry needed.

The problem it solves

You have something that is expensive to compute, and needed in several unrelated places during one request — a template tag, a model method, a serializer, a signal handler:

# views.py
settings = SiteSettings.objects.get()

# templatetags/theme.py
settings = SiteSettings.objects.get()   # same query again

# models.py
settings = SiteSettings.objects.get()   # and again

The usual fixes are awkward: thread request through every function, hang attributes off request, or reach for a global cache and then worry about invalidation.

With stash, each call site asks for the value by name and the first one pays:

import stash

def get_site_settings():
    return stash.get_or_set("site_settings", lambda: SiteSettings.objects.get())

Where this fits

Reach for stash when a value is expensive, needed in more than one place during a single request, and awkward to get to from where you are:

• A request-derived value needed somewhere without request. Middleware resolves the current tenant from the hostname; a model manager, a permission check, and a signal handler all need it too, but none of them have request in scope.

  def get_current_tenant():
      return stash.get_or_set("tenant", resolve_tenant_from_request)
  

• A check that fans out across a page. A changelist renders 50 rows and calls can_edit(obj) for each. If can_edit starts with something request-wide — "is this user a reviewer this month" — that shouldn't be recomputed 50 times.
• You're about to write request._cached_thing = .... This pattern already exists in most Django codebases: stash something on request in middleware, read it back everywhere else. It works, but it only works where request is reachable, and it leaks the caching detail into every call site. stash.get_or_set is the same idea, usable from anywhere, without a request reference.
• A value that must be refreshed mid-request after a write. Read settings early; a view updates them; later code in the same request must see the new value. One stash.clear("site_settings") call after the write handles it — see clear below.
• Batch scripts, one memo per unit of work. Wrap each row/item in stash_scope() so lookups inside it are cheap, and nothing survives to the next item.

Where this doesn't fit

• You want the answer shared across requests, workers, or deploys. That's Django's cache framework (django.core.cache, backed by Redis/Memcached/the DB). Stash never outlives one scope — put it in front of that cache as L1 if you want both.
• The value needs to reach other processes. Stash is per-process, per-scope. One worker's stash tells another worker nothing.
• A pure function with no invalidation need, no request in the picture. functools.lru_cache is simpler and doesn't need a scope at all.

Alternatives

The last row is the trap: a hand-rolled threading.local() or asgiref.Local() looks identical to stash until a worker process reuses its thread for a second request and the old value is still sitting there. Stash's storage is the same mechanism (asgiref.local.Local), but the lifetime is never left to memory — StashMiddleware opens and closes the scope on every single request, so there's no window where a stale value can survive into the next one.

django-request-cache takes the same idea a step further: instead of exposing one named value, it makes the whole request object reachable from anywhere first (via django-userforeignkey's get_current_request()), then hangs a cache off it as an attribute. That's an extra dependency, and a much bigger object made globally available than most call sites need. Stash's storage never holds request — only the specific values you chose to stash, by name.

Django's cache framework (django.core.cache) is still the right choice the moment a value needs to survive past one request — nothing here replaces it. The trade-off in the table above is the one to remember: reach for the cache framework when a value is shared across requests or processes, and put stash in front of it when the same value is read more than once inside a single request.

Usage

get_or_set

import stash

def get_feature_flags():
    return stash.get_or_set("feature_flags", load_feature_flags_from_db)

• First call in a request: runs load_feature_flags_from_db(), stores the result, returns it.
• Later calls in the same request: returns the stored result. The loader is not called.
• After the request ends: the stored value is gone.

memoize

Same thing, as a decorator:

import stash

@stash.memoize
def get_exchange_rate(currency):
    return ExchangeRate.objects.get(currency=currency).rate

get_exchange_rate("EUR") and get_exchange_rate("USD") are remembered separately (the key is built from the arguments). Use @stash.memoize(key="...") for a fixed key that ignores arguments.

get, set, clear

stash.set("user_permissions", perms)
stash.get("user_permissions")            # -> perms, or None
stash.get("missing", default=[])         # -> []

stash.clear("user_permissions")          # forget one value
stash.clear()                            # forget everything for this request

clear is what you call after writing to the underlying data, so later reads in the same request see the new state:

def update_site_settings(**changes):
    SiteSettings.objects.filter(pk=1).update(**changes)
    stash.clear("site_settings")

Outside a request

Nothing is stored unless a scope is open. In a management command, Celery task, or shell:

stash.get_or_set("k", loader)   # just calls loader() every time
stash.set("k", value)           # does nothing
stash.get("k")                  # -> None

That is deliberate: a long-lived worker never accumulates stale values by accident.

If you want the same per-unit-of-work behaviour there, open a scope yourself:

with stash.stash_scope():
    process_batch()   # values remembered for this block only

Behaviour in one table

Notes

• Values are stored and returned as shallow copies. Mutating what you get back does not change what is stored. Don't rely on identity.
• Stash is an L1 in front of whatever you already do. If you also want cross-process sharing, keep using Django's cache as L2 inside your loader.
• Works under WSGI and ASGI, with sync or async views. The middleware is sync- and async-capable, so it does not force Django to adapt the rest of the chain. Storage is asgiref.local.Local.

Development

cd django-stash
python -m venv .venv && source .venv/bin/activate
pip install -e ".[testing,development]"
python testmanage.py test