Reference counting, garbage collection, profiling, and where interpreter overhead dominates.
3 questions in Python.
The cache lives on the class-level function and its keys include self, so every instance the method touches stays strongly referenced and is never collected; with maxsize=None or functools.cache that memory leak is unbounded. Cache per instance with cached_property or an instance dict, or cache plain values.
Into per-object overhead: in CPython on a 64-bit build every object carries a 16-byte header, every field is itself a boxed object reached through an 8-byte pointer, and each instance has a dictionary. Slots remove the dictionary, and a columnar layout removes the objects. Use this memory layout answer to show the decision, trade-off, and evidence rather than a memorised definition.
CPython frees an object the instant its reference count reaches zero, so steady growth is usually something still holding a reference rather than a leak. The cycle collector reclaims only reference cycles. Measure with tracemalloc first, then use __slots__ or generators to cut per-object and peak cost.