This is clearly one for me to abandon! Thanks for the explanations. John
On Mon, Jan 17, 2022 at 7:04 PM Paul Moore <p.f.mo...@gmail.com> wrote: > On Mon, 17 Jan 2022 at 18:51, John Sturdy <jcg.stu...@gmail.com> wrote: > > > > My idea is to support the style in which each variable comes into > existence at a single well-defined point, whatever path is taken through > the code, and so in the case of that example, it would be encouraging the > use of conditional expressions. > > But that's a style that Python explicitly rejected right back when it > was first designed, and it's fundamental to the language that you > *don't* explicitly declare variables. So sorry, but it's never going > to happen[1]. > > If you want to be really precise, technically "the style in which each > variable comes into existence at a single well-defined point" is > actually what Python already does. The "well-defined point" is the > start of the scope (function or class definition) where the variable > is used, though, and not at some new "let" keyword. > > To see this, look at the following: > > >>> def f(): > ... print(n) > ... n = 1 > ... > >>> f() > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > File "<stdin>", line 2, in f > UnboundLocalError: local variable 'n' referenced before assignment > > The variable "n" exists when the print statement runs (it's unbound, > but it exists - that's what the exception says), and that's because > the variable comes into existence at the *start* of the scope > (function). > > And the choice to only have a limited number of ways to define scopes > is *also* a fundamental design principle of Python, so arguing that > suites should each define their own scope won't get you very far > either. > > Essentially, you're proposing to change Python to no longer be Python, > in some fairly fundamental ways. Don't be surprised if you get very > few supporters for your idea... > > Paul > > [1] In theory, the SC could say that such a change is fine, but I > can't see that ever happening. >
_______________________________________________ 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/WNJSIYW6EGAV5PHQK2JWYA7EXEY4YJNH/ Code of Conduct: http://python.org/psf/codeofconduct/
