> [Guido]
> > ...
> > Some examples where no parentheses are needed (note that a comma binds
> > less tight than a conditional expression -- same as for lambda):
> >
> > x = if 1 then 2 else 3, y
[Tim]
> Also
>
> x = if 1 then 2 else 3,
>
> which sets x to the singleton tuple (2,). This is an old potential
> confusion, though, much the same as the current
>
> x = 2 or 3,
>
> (which also sets x to (2,)).
These don't bother me any more than
x = 2,
does.
> > ...
> > Some examples where parentheses *are* required:
> >
> > (if 1 then 2 else 3) + 4
>
> But that's because it's a top-level expression beginning with "if", not
> because of the "+", right? In the patched Python, this works fine:
>
> >>> x = if 0 then 2 else 3 + 4
> >>> x
> 7
> >>>
But it groups differently: the 'else' part is '3 + 4' here. Try 'if
1'. :-)
> OTOH, these seem odd:
>
> >>> 4 + if 1 then 2 else 3
> File "<stdin>", line 1
> 4 + if 1 then 2 else 3
> ^
> SyntaxError: invalid syntax
That's too much work for the parser to get right. And you'd get
anomalies like
3 * if 1 then 2 else 3 + 4
-- how should this group?
> >>> x = 4 + if 1 then 2 else 3
> File "<stdin>", line 1
> x = 4 + if 1 then 2 else 3
> ^
> SyntaxError: invalid syntax
> >>>
>
> I say "odd" because there's no question about what they mean.
Only because the examples are so simply.
> > a[(if i then 2 else 3) : 4]
> >
> > In some situations I'm not sure what's right; The un-parenthesized
> > form looks weird although it's not neede to avoid ambiguity:
> >
> > if (if 1 then 2 else 3): pass
> > print (if 1 then 2 else 3)
>
> OTOH,
>
> print >> sys.stderr, if 1 then 2 else 3
> and
> print 4, if 1 then 2 else 3
>
> don't look particularly weird but also raise SyntaxError.
>
> As a matter of taste, I was most surprised by the
>
> 4 + if 1 then 2 else 3
>
> examples.
They act the same as lambda in this respect.
Because the conditional *ends* in something that "pulls in" all
following binary operators and their operands until it hits a ")",
I find it safer not to let it accept an operator at the front.
--Guido van Rossum (home page: http://www.python.org/~guido/)
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