On Fri, Sep 18, 2020 at 1:38 AM Eric V. Smith <e...@trueblade.com> wrote: > > In general, there's no way to start with a format specifier string and > from it get the type of the object that it should be applied to. For > example, any string without %'s is a valid datetime format specifier (of > dubious value, but such is life). Perhaps a better example is decimal > vs. float. What if I want %.2f to return a decimal? Would that just not > be possible? > > So I think you'd have to limit this to a small set of built-in types. > > In general, I think overloading f-strings as assignment targets would be > confusing. But I've been wrong before. >
It doesn't have to be absolutely identical, just as long as it's mostly parallel. Consider C's printf and scanf formats; any whitespace in scanf matches any whitespace, and the integer handlers are always happy to accept a leading plus sign (which has to be specifically requested in printf). Conversely, scanf can be more restrictive, eg %[a-z] which will match some sequence of lowercase ASCII letters. IMO printf notation (what in Python does with str % ...) is better suited to this than Python's .format() notation (which f-strings also use). But the advantages of f-strings would also apply here. Maybe the best way would be the tagged version of percent formatting? >>> x, y = 1, 2 >>> "==> (%(x)d, %(y)d)" % globals() '==> (1, 2)' Theory: "==> (%(x)d, %(y)d)" = "==> (1, 2)" could assign x=1 and y=2. (It'd want to have some sort of tag to show what's going on, but not f"..." since it's not an f-string.) PEP 622 pattern matching may be relevant here. 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/PYETEF73PH2I6SN4UBWSEVJ5MH5IYFTA/ Code of Conduct: http://python.org/psf/codeofconduct/
