On Thu, Aug 1, 2013 at 6:35 PM, Ian Kelly <ian.g.ke...@gmail.com> wrote: > yield was a statement before it became an expression, and the syntax > "yield x, y, z" was (and still is) perfectly legal, with all three > expressions (technically a single tuple expression) being governed by > the yield. That is to say, "yield x, y, z" and "yield (x, y, z)" are > semantically equivalent. When it became an expression, in order to > preserve this equivalence, that meant that the yield expression needed > to bind even less tightly than the comma. In terms of the grammar, > yield needed to take an expression_list, not just an expression. > > There are only three places in the grammar where expression_lists are > used without enclosing them in brackets: expression statements (in > this case analogous to the yield statement), the return statement (not > normally used to return a value in a generator), and the assignment > statements. So for consistency and clarity the rules for > parenthesizing yield statements are basically adopted from the > existing rules for parenthesizing expression_lists.
Ahh, right. That makes good sense. If this were being created anew now, would yield be made to bind more tightly than the comma? That would mean that yield x, y, z # Yield a tuple would need to be written as: yield (x, y, z) which wouldn't, in my opinion, be a bad thing. (It'd probably catch a few people out, but a linter could notice that a tuple is being created and ignored.) So this is a bit of a wart, but it's for backward compatibility. Right? ChrisA -- http://mail.python.org/mailman/listinfo/python-list
