Steven D'Aprano writes:
> On Sun, 29 Sep 2013 12:35:17 +0300, Jussi Piitulainen wrote:
>
> > try:
> > ...
> > except socket.gaierror as e:
> > # watch out, a composition of bad advice (on demand) city, host = (
> > ('city' in locals() or "blabla"),
> > ('host' in locals() or "blablabla") )
>
> Bad advice, and buggy as well.
>
> py> city = "New New York"
> py> ('city' in locals() or "Blah blah")
> True
>
> Oh man, can you imagine Nikos trying to debug that?
Thanks. Sorry. This hurts. I didn't mean it to be buggy.
Let's see. The task is to assign a default value to city and host, if
they haven't a value yet; on one line (which I take to mean one
statement); in an "except" block where we may not know which
assignment failed in the "try" block; without "if"; but "or" is
allowed.
But the logic I was trying to implement is
city, host = ( (city if 'city' in locals() else "default city"),
(host if 'host' in locals() else "default host") )
which uses an "if". The old tricks of using "or" and stuff for this
would surely go too far.
I know!
city, host = ( locals().get('city', "default city"),
locals().get('host', "default host") )
Testing if the variables only exists when actually assigned:
>>> def foo(x, y):
... if x: foo = None
... if y: bar = "bar"
... return locals()
...
>>> foo(False, False)
{'y': False, 'x': False}
>>> foo(False, True)
{'y': True, 'x': False, 'bar': 'bar'}
Seems so.
What a monster, though. I don't even want to know if this, too, is
buggy in some way. It looks fragile.
Nikos, don't do this. The way to test if an assignment failed is to
use a try-catch. The way to know which one failed is to put each in
its own try-catch.
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