22.04.21 10:21, Stephen J. Turnbull пише: > @serhiy Moving my speculative discussion to python-ideas. CC as > courtesy, comment from you is welcome but not necessarily expected. > > Serhiy Storchaka writes: > > > format() without format specifier and str() should return the same > > value in general, otherwise it will confuse users. > > I think this is a good rule of thumb because it's a very plausible > default for format(), and easy to explain. > > But then what is the purpose of format()? Why not just give str() the > functionality of format(), and deprecate format() for future use? Or > vice versa, format() might be the better name, but the backward > compatibility implications given the pervasive use of str() would be > awesome, and not in a good way.
Technically, because the second argument of str() means encoding. So you would need either make format specifier a third positional parameter, str(price, None, None, '8.2f') or make it a keyword-only parameter, str(price, format_spec='8.l2'). Both are look ugly. And since a format specifier is mutually incompatible with encoding and errors, it is clear that there should be two distinct functions. Also, all existing __str__ methods do not accept additional arguments. There is no way to pass format specifier to it. So we need a new special method. We could name it __str_ex__, but __format__ seems a better name. > Given how pervasive both str and format are, and the fact that str > also has both .format() and .__format__ methods, I guess I'm asking > for a lot of trouble. But this plethora of approaches to providing a > string presentation of an object seems designed to confuse users, and > it's not clear to me that trying to maintain str(thing) == format(thing) > necessary helps dissolve that confusion. It is not hard to maintain because object.__format__ just calls __str__. If you do not implement __format__, you get it by default. If you implement __format__ you are free to do what you want. And usually, if you implement addition and multiplication, you have to maintain thing+thing == thing*2, but it does not mean that we need to merge addition and multiplication into single operation. _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/FIJCVRUCFADXE22HJZTK2RBPJLELPIKJ/ Code of Conduct: http://python.org/psf/codeofconduct/
