In msg142098  Ezio said:
> Keep in mind that we should be able to access and use lone surrogates too, therefore:
> s = '\ud800'  # should be valid
> len(s)  # should this raise an error? (or return 0.5 ;)?

I say:
For streams and data types in which lone surrogates are permitted, a lone surrogate should be treated as and counted as a character (codepoint).

For streams and data types in which lone surrogates are not permitted, the assigned should be invalid, and raise an error; len would then never see it, and has no quandary.