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).
I've posted a new version of the code in issue 24965. I'll update the
PEP itself sometime this weekend.
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