Eric V. Smith <e...@trueblade.com> added the comment:
About translating ":s" to "":
> The library seems
willing to do this for the empty format string, but not when the client
code specifically asks for a string....
You're not asking for a string when you specify ":s". You're asking the object
to interpret "s" however it wants. For example, if the object is a datetime,
you're asking for the output to be "s":
>>> f'{datetime.datetime.now():s}'
's'
versus:
>>> f'{datetime.datetime.now()}'
'2018-08-22 10:27:25.188891'
It's precisely because we want to let the object interpret the string that
Python no longer guesses as to what you might mean.
For example, say you have a MyDate object, that doesn't support __format__, and
you want Python to decide that format(MyDate(), 's') means is the same as
format(MyDate(), ''). But later you decide that you want the format strings to
call strftime (like datetime does). You couldn't do that without breaking
existing usage of your library.
This actually happened with complex when I added complex.__format__.
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue34425>
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