ABCMeta.__new__ calls `getattr(value, "__isabstractmethod__", False)` many times.
https://github.com/python/cpython/blob/0f31c74fcfdec8f9e6157de2c366f2273de81677/Lib/abc.py#L135-L142

Since metaclass is used by subclasses, it checks all members of all subclasses (including concrete class).

But getattr() and hasattr() is inefficient when attribution is not found,
because it raises AttributeError and clear it internally.

I tried to bypass AttributeError when tp_getattro == PyObject_GenericGetAttr.
Here is quick micro benchmark:

$ ./python-patched -m perf timeit --compare-to=`pwd`/python-master -s 'def foo(): pass' 'hasattr(foo, "__isabstractmethod__")'python-master: ..................... 385 ns +- 2 ns
python-patched: ..................... 87.6 ns +- 1.6 ns

Mean +- std dev: [python-master] 385 ns +- 2 ns -> [python-patched] 87.6 ns +- 1.6 ns: 4.40x faster (-77%)

(I added Ivan to nosy list because he may implement C version of ABC.)