PY-CACH0002 · cached_instance_method

Avoid retaining object instances in function-wide method caches.

This is a deterministic rule for python. Read its implementation.

Definition

Inspect direct class methods decorated with functools.cache or functools.lru_cache, including called decorator forms and qualified names. Report ordinary instance methods, which are the ones binding neither classmethod nor staticmethod, because Python includes self in the cache key and retains cached arguments until eviction or an explicit clear. Use cached_property for a zero-argument value owned by one instance. Move a computation independent of instance identity to a module-level cached function.

Evidence

Each finding identifies the class, method, cache decorator, and complete source range. The Boolean result identifies one cached instance method.

Exceptions

Static methods and class methods are excluded because they do not retain ordinary instances. Generated and vendored code can be excluded by path. A deliberately bounded instance cache may disable this preference when its ownership and clearing behavior are explicit.

Examples

Bad

@lru_cache(maxsize=128)
def parse(self, text: str) -> Node:
    return self.parser.parse(text)

Good

@cached_property
def schema(self) -> Schema:
    return build_schema(self.fields)

@cache
def tokenizer(model: str) -> Tokenizer:
    return Tokenizer.load(model)

References

• Cites “The Python Standard Library”, functools.lru_cache. Open reference
• Cites “Python FAQ”, caching methods. Open reference