gh-146086: Clarify sys.getsizeof() docstring regarding additional overhead

[merkulovlad]

This change clarifies the short built-in documentation for sys.getsizeof().

The full documentation already explains that getsizeof() calls __sizeof__() and may add additional overhead (e.g., for the garbage collector). However, this distinction is not visible from the short help output (help() / pydoc).

This change adds a short clarification to reduce potential confusion.

This is a documentation-only change and does not affect runtime behavior. No NEWS entry is needed.

• Issue: Clarify the diffrence between object.__sizeof__() and sys.getsizeof() in short documentation/help output #146086

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[sergey-miryanov]

I'm not sure it is worth doing. Added message doesn't no clarify the difference IMO, because there can be more extra data, that not calculated.

cc @picnixz

[merkulovlad]

Thanks for the feedback!

I see your point that additional overhead is not limited to the garbage collector and that both __sizeof__() and sys.getsizeof() do not necessarily reflect the full memory usage.

My intention was mainly to reduce the potential confusion from the short help text, where __sizeof__() and sys.getsizeof() may appear equivalent.

Would it make sense either to:

1. remove the specific reference to the garbage collector, or
2. use a more general wording, for example:

The result may include additional memory overhead and may not reflect the total memory consumption of the object

Happy to adjust the wording based on your preference.