On Mon, Dec 28, 2020 at 9:22 AM Joao S. O. Bueno <jsbu...@python.org.br> wrote: > > I agree - the three builtin methods are almost the same (not sure if > there is any difference at all),
Yes - they all check if the string matches a particular set of characters. > while there is no trivial way to check for a valid > float, or otherwise a chosen representation of a decimal number without > resorting > to a try-except statement, or complicated verification schemes that have > to deal with a lot of corner cases. If you want to know whether the float() call will throw, the best way to check is to call float() and see if it throws. > For validity one has to check if there are only digits - and decimal points - > and the "-" unary sign. What if there is more of a "." in the string? > what if the "-" is not the first character? > And besides validity checking, there are also validity choices: > What if an unary "+" is present? Whitespace ok? "_" as digit separator ok? > scientific exponential notation accepted? What about Inf and Nan literals? > What about taking into account the locale setting? > > But maybe, instead of yet another str method, a "parsefloat" function > that could get arguments and sensitive defaults for some choices - > it could live in "math" or "numbers". How about a built-in called "float", which either returns the floating-point value represented by the string, or signals an invalid string with an exception? > I think it would be preferable than, say, adding a lot of options > to the `float` constructor. These are the options I can think > of the top of my mind: YAGNI. If you want to allow specific subsets of valid options, it's not that hard to do your own validation. > The return value would consitss of a boolean, where True would indicate > success, and then the number. > Or it could return a single float, returning a NaN in case of parsing error. Or it could raise in the case of parsing error. That's the Pythonic way. ChrisA _______________________________________________ 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/F5TGEV5V4ZKAPSD5AI62EJ6YZRKQQPFQ/ Code of Conduct: http://python.org/psf/codeofconduct/
