inhouse

Zero-dependency, in-process TTL cache for Python. One decorator, stampede-safe, LRU-bounded. For when Redis is a meeting you don't want to have, or when you need to avoid yet another deployment. Designed to be simple and effective without bloat or complexity for developers.

Designed for easy use with FastAPI applications, though FastAPI integration is entirely optional.

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Install

The package is published on PyPI as inhouse-cache. Imports use inhouse (e.g. from inhouse import MemoryStore).

Core:

pip install inhouse-cache

With FastAPI helpers (fastapi_cache, lifespan sweeper):

pip install inhouse-cache[fastapi]

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Quick Start Usage

Core (any Python project)

from inhouse import MemoryStore, inhouse_cache

store = MemoryStore(max_size=1024, default_ttl=60)

@inhouse_cache(store=store)
async def load_user(user_id: int) -> dict[str, int]:
    return {"user_id": user_id}

Works with both async def and def callables.

FastAPI Use Case

import asyncio
from fastapi import FastAPI
from inhouse import MemoryStore
from inhouse.fastapi import create_lifespan, fastapi_cache

store = MemoryStore(max_size=1024, default_ttl=60)
app = FastAPI(lifespan=create_lifespan(store))

@app.get("/items/{item_id}")
@fastapi_cache(store=store)
async def get_item(item_id: int) -> dict[str, int]:
    await asyncio.sleep(0.1)  # expensive work
    return {"item_id": item_id}

Requires pip install inhouse-cache[fastapi].

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Features

Core (zero dependencies)

• TTL cache with lazy expiry on read
• LRU eviction when max_size is exceeded
• Per-key singleflight stampede guard — concurrent misses on the same key coalesce to one computation. Backend errors propagate to all waiters; client disconnect on the leader no longer aborts in-flight cache population for followers
• Deterministic cache keys — canonical JSON serialization with type-qualified fallbacks for custom objects. Keyword argument order and Request subclasses don't cause spurious cache misses
• Thread-safe store for sync and async callables
• Fixed, store-default, or callable TTL on each cache write
• Opt-in copy_on_read on MemoryStore — deep-copy cached values on read to prevent caller mutation from corrupting the cache

Optional FastAPI extra (pip install inhouse-cache[fastapi])

• @fastapi_cache with Request/Response-aware cache keys
• @fastapi_cache(key_builder=...) — custom key builder for domain objects or database models without fighting the default JSON encoder
• Background expiry sweeper via FastAPI lifespan helpers
• Clean lifespan shutdown — background sweeper cancels without noisy tracebacks

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What's New in v0.1.2

• FastAPI integration package — inhouse.fastapi is now a package (keys, decorator, lifespan submodules), establishing the inhouse/<integration>/ pattern for future backends. Public imports are unchanged.
• MemoryStore(copy_on_read=True) — opt-in deep copy on get() so callers cannot mutate cached dicts/lists and corrupt state for other requests.
• Type-qualified key fallback — custom objects with identical str() representations no longer collide in cache keys; distinct types get distinct keys.
• @fastapi_cache(key_builder=...) — pass a custom key builder for domain objects or database models without fighting the default JSON encoder.
• Async singleflight cancellation shield — if the leader HTTP client disconnects mid-compute, the backend work continues and populates the cache for concurrent followers waiting on the same key.

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Configuration Reference

MemoryStore

from inhouse import MemoryStore

store = MemoryStore(max_size=1024, default_ttl=60)

Parameter / attribute	Type	Default	Description
max_size	int	1024	Maximum number of entries before LRU eviction
default_ttl	float | None	None	Default TTL in seconds for store.set() and decorators that omit ttl_seconds
copy_on_read	bool	False	When True, get() returns copy.deepcopy() of cached values so callers cannot mutate the store
default_ttl (property)	float | None	—	Mutable at runtime; affects future writes only
size	int (read-only)	—	Current number of cached entries

Store methods:

Method	Description
get(key, *, default=MISS)	Return a cached value, or default on miss/expiry. Deep-copies when copy_on_read=True
set(key, value, ttl_seconds=None)	Write a value; uses default_ttl when ttl_seconds is omitted
delete(key)	Remove one entry
clear()	Remove all entries
purge_expired()	Proactively delete expired entries
keys()	List current cache keys

@inhouse_cache / cache()

Core decorator. Works with both async def and def callables.

from inhouse import MemoryStore, inhouse_cache, make_cache_key

store = MemoryStore(default_ttl=60)

@inhouse_cache(
    ttl_seconds=60,              # optional — see Dynamic TTL below
    store=store,                 # optional — defaults to a module-level store
    key_builder=make_cache_key,  # optional — custom cache key strategy
    exclude_types=(object,),     # optional — types omitted from key material
)
async def load_user(user_id: int) -> dict[str, int]:
    return {"user_id": user_id}

Parameter	Type	Default	Description
ttl_seconds	float | Callable[[], float] | None	None	TTL in seconds for each cache write. See Dynamic TTL.
store	MemoryStore | None	module default	Cache instance to read/write
key_builder	Callable[..., str]	make_cache_key	Builds the cache key from function identity + arguments. Non-JSON-serializable arguments fall back to module.qualname:str(value)
exclude_types	tuple[type, ...]	()	Argument types excluded from key material (e.g. request objects)

inhouse_cache is an alias for cache.

Global default store helpers:

from inhouse import configure_default_store, get_default_store

store = MemoryStore(default_ttl=120)
configure_default_store(store)

@inhouse_cache()  # uses the configured default store + its default_ttl
async def load_config() -> dict[str, str]:
    ...

@fastapi_cache (optional — requires inhouse-cache[fastapi])

FastAPI-friendly wrapper around inhouse_cache. Automatically excludes Starlette Request and Response objects from cache keys.

from inhouse.fastapi import create_lifespan, fastapi_cache

store = MemoryStore(max_size=512, default_ttl=60)
app = FastAPI(lifespan=create_lifespan(store, sweep_interval=30.0))

@app.get("/items/{item_id}")
@fastapi_cache(store=store)
async def get_item(item_id: int) -> dict[str, int]:
    ...

Parameter	Type	Default	Description
ttl_seconds	float | Callable[[], float] | None	None	Same semantics as @inhouse_cache
store	MemoryStore | None	module default	Cache instance to read/write
key_builder	Callable[..., str] | None	make_fastapi_cache_key	Custom key builder. Defaults exclude Starlette Request/Response; override delegates that responsibility to you

Custom key_builder functions replace the FastAPI-aware default. To keep Request/Response exclusion, delegate to make_fastapi_cache_key or pass your own exclude_types.

Lifespan / Background Cleanup (optional — requires inhouse-cache[fastapi])

from inhouse.fastapi import create_lifespan, inhouse_lifespan

# Option A: pass directly to FastAPI
app = FastAPI(lifespan=create_lifespan(store, sweep_interval=30.0))

# Option B: use inside your own lifespan
async with inhouse_lifespan(store, sweep_interval=30.0):
    ...

Parameter	Type	Default	Description
store	MemoryStore	required	Store to sweep for expired entries
sweep_interval	float	30.0	Seconds between background purge runs

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Dynamic TTL

TTL is resolved when a value is written to the cache (on a miss), not on every read. Changing TTL settings does not retroactively extend entries already stored.

1. Fixed TTL (per route)

@inhouse_cache(60, store=store)
async def load_user(user_id: int) -> dict[str, int]:
    ...

Always expires 60 seconds after the value is cached.

2. Store Default (mutable at runtime)

store = MemoryStore(default_ttl=60)

@inhouse_cache(store=store)
async def load_config() -> dict[str, str]:
    ...

# Later — affects future cache writes only
store.default_ttl = 300

Omitting ttl_seconds on the decorator uses store.default_ttl. If both are missing, inhouse raises ValueError.

store.default_ttl is safe to change at runtime from other threads; new writes pick up the updated value atomically.

3. Callable TTL (evaluated on each write)

settings = {"cache_ttl": 60}

@inhouse_cache(lambda: settings["cache_ttl"], store=store)
async def load_dashboard() -> dict[str, str]:
    ...

settings["cache_ttl"] = 300  # next cache miss uses 300 seconds

Useful for feature flags, config files, or environment-driven TTL without redeploying.

Priority Order

When a cache miss is written, TTL is resolved as:

1. Callable ttl_seconds() result, if a callable was passed
2. Fixed ttl_seconds float, if provided
3. store.default_ttl, if set
4. Otherwise → ValueError

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When to Use inhouse

Scenario	inhouse	Redis	fastapi-cache2
Single-node FastAPI prototype	Great	Overkill	Great
Zero external infrastructure	Yes	No	Depends on backend
Distributed multi-instance cache	No	Yes	Yes (with Redis)
Decorator-first developer UX	Yes	No	Yes

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Important Limitations

inhouse is per-process memory. If you run uvicorn main:app --workers 4, each worker maintains its own independent cache. That keeps the design simple and avoids shared infrastructure. It is not a distributed cache.

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Architecture

Core API

The core package has no runtime dependencies. Import from inhouse directly:

from inhouse import MemoryStore, configure_default_store, inhouse_cache, make_cache_key

See the Configuration Reference for full decorator and store options.

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License

MIT