On Wed, Jul 4, 2018 at 6:36 AM Steven D'Aprano <st...@pearwood.info> wrote: > > On Wed, Jul 04, 2018 at 01:03:02AM -0700, Devin Jeanpierre wrote: > > > The PEP doesn't talk about it, but FWIW, Go and C++17 if statements > > allow you to put arbitrary simple statements in the suite header, and > > by doing that, solves all the issues you and the PEP mentioned. > > Whether they solve "all the issues" discussed in the PEP is doubtful, > since they're entirely limited to just if statements.
The only issue that PEP 572 has with limiting to if statements is: "Disadvantages: Answers only a fraction of possible use-cases, even in if/whilestatements." The Go/C++17 syntax resolves that (while still being limited to if statements and while statements -- the primary use cases AFAIK, and the only ones Nathaniel agrees with). > > In Python it'd look like this: > > > > if x = expr(); x < 0: > > do_stuff() > > > That's even more doubtful, since the semicolon in Python already has a > meaning of separating statements on a line. That could be equivalent to: > > if x = expr() > x < 0: > do_stuff() > > which would clearly have to be a syntax error. *Two* syntax errors. > > Python's parser is restricted to LL(1) by design, so treating semicolons > in "if" statements as a special case might not even be possible. > But even if it is possible, not only would this special case > break the Zen, but it would be UGLY too. It isn't a special case, and it's still LL(1). Once you encounter an "if", you parse n simple statements separated by a ";", until you reach a colon. Where LL(1) runs into trouble is that last statement must be an Expr statement, but that can be checked after parsing (e.g. during compilation). I don't understand why you think this is "clearly" a syntax error. (So is ":=", if you restrict yourself to the current Python syntax.) As for ugly... well, compare: while (kv := x.pop())[0] is not None: foo(kv[1]) while k, v = x.pop(); k is not None: foo(v) if (v := d[k]) == _EOF: return None if v = d[k]; v == _EOF: return None I like ":=" when it is the only thing in the expression: "if a:= b:" etc. Every other time I would prefer C++/Go's syntax. -- Devin _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
