PEP 757: edit rejected ideas (mpz_import/export-like API) (python#4126)

peps/pep-0757.rst

@@ -452,11 +452,17 @@ API example::
     int PyLong_Export(PyLongObject *obj, PyLongLayout layout, void *buffer);
     PyLongObject *PyLong_Import(PyLongLayout layout, void *buffer);
 
-This might work for the GMP, as this it has :c:func:`!mpz_limbs_read()` and
-:c:func:`!mpz_limbs_write()` functions, that can provide required "buffers".
+This might work for the GMP, as it has :c:func:`!mpz_limbs_read()` and
+:c:func:`!mpz_limbs_write()` functions, that can provide required access to
+internals of :c:struct:`!mpz_t`.  Other libraries may require using temporary
+bufferes and then mpz_import/export-like functions on their side.
 
 The major drawback of this approach is that it's much more complex on the
-CPython side (i.e. actual conversion between different layouts).
+CPython side (i.e. actual conversion between different layouts).  For example,
+implementation of the :c:func:`PyLong_FromNativeBytes()` and the
+:c:func:`PyLong_AsNativeBytes()` (together provided restricted version of the
+required API) in the CPython took ~500 LOC (c.f. ~100 LOC in the current
+implementation).
 
 
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