On 09/28/2015 01:57 PM, Guido van Rossum wrote:
On Mon, Sep 28, 2015 at 12:53 PM, Carl Meyer <carl@oddbird.net <mailto:carl@oddbird.net>> wrote:
On 09/28/2015 01:43 PM, Carl Meyer wrote: [snip] > I assume that the short-circuiting would follow the precedence > order; that is, nothing with looser precedence than member and index > access would be short-circuited. So, for example, > > foo?.bar['baz'].spam > > would short-circuit the indexing and the final member access, translating to > > foo.bar['baz'].spam if foo is not None else None > > but > > foo?.bar or 'baz' > > would mean > > (foo.bar if foo is not None else None) or 'baz' > > and would never evaluate to None. Similarly for any operator that binds > less tightly than member/index access (which is basically all Python > operators).
For a possibly less-intuitive example of this principle (arbitrarily picking the operator that binds next-most-tightly), what should
foo?.bar**3
mean?
It's nonsense -- it means (foo?.bar)**3 but since foo?.bar can return None and None**3 is an error you shouldn't do that. But don't try to then come up with syntax that rejects foo?.bar**something statically, because something might be an object implements __rpow__.
And I still don't see why this "principle" would be important.
The only "principle" in question here is "nothing with looser precedence than member and index access would be short-circuited," and you seem to agree with it. I was just making sure that foo?.bar**3 couldn't possibly mean (foo.bar**3 if foo is None else None) and I'm glad it couldn't. Carl