On 19 September 2015 at 21:03, Eric V. Smith <e...@trueblade.com> wrote:
> While finishing up the implementation of PEP 498, I realized that the
> PEP has an error. It says that this code:
>
> f'abc{expr1:spec1}{expr2!r:spec2}def{expr3:!s}ghi'
>
> Is equivalent to:
>
> 'abc' + expr1.__format__(spec1) + repr(expr2).__format__(spec2) + 'def'
> + str(expr3).__format__('') + 'ghi'
>
> But that's not correct. The right way to call __format__ is:
>
> type(expr1).__format__(expr1, spec1)
>
> That is, the lookup of __format__ is done on the type, not the instance.
>
> Instead of calling __format__, I've changed the code generator to call
> format(expr1, spec1). As an optimization, I might add special opcodes to
> deal with this and string concatenation, but that's for another day (if
> ever).Does this mean overriding format at the module level or in builtins will affect the way f-strings are evaluated at runtime? (I don't have a strong preference one way or the other, but I think the PEP should be explicit as to the expected behaviour rather than leaving it as implementation defined). Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
