I mean approximately local to one line of source code. Perhaps the unpopular opinion based on your reaction. :)
More specifically, for a simple statement (with no trailing colon), there is one scope enclosing everything in the statement. For a compound statement, composed of multiple clauses, where each clause has a header (ending with a colon) and a suite, there are N non-overlapping scopes, one scope for each of the N clause headers. The scope is limited to the header only and does not include the suite. In considering a 'for' loop, I'd advocate for keeping the scope of the expression_list separate from the target_list, since I can't think of a reasonable case where the target_list would want to reference something from the expression_list. So the following code would have a NameError for magic_index in the target_list: > # NameError: name 'magic index' is not defined > for my_array[magic_index] in list_of_lists[(f(...) as magic_index)]: > ... That's pretty bizarre code, using a fixed index of an array as an iteration variable. The only other type of 'for' loop target that might try to use a named expression from the expression_list is a slice expression, which would be even more bizarre code. Best to make bizarre cases into errors. Cheers, -- David Foster | Seattle, WA, USA On Sat, Mar 17, 2018 at 12:13 AM, Chris Angelico <ros...@gmail.com> wrote: > On Sat, Mar 17, 2018 at 5:49 PM, David Foster <davidf...@gmail.com> wrote: > > (3a) With a header-limited scope (in proposal #1 above), I advocate that > a > > named expression should NOT be able to shadow other variables, giving a > > SyntaxError. I can't think of a reasonable reason why such shadowing > should > > be allowed, and preventing shadowing may eliminate unintentional errors. > > Header-limited scope is hard to define. Do you mean expression-local? > (Also hard to define.) Do you mean local to one line of source code? > Definitely not. And what happens with a 'for' loop - part of its > header gets run after each loop iteration but still kinda references > stuff that was done once-only before the loop started. > > ChrisA > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ > -- David Foster
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