[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
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,)).
> ...
> 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
>>>
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
>>> 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.
> 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.
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