Hmm, checking my code, you are right, the idiom I was actually using (in one
very old module still in my codebase, and which still works ;) ) was
(paraphrased):
NULL = (1,) # why doesn't () work? Get with it Guido ;)
As for cheating... no, actually, I didn't feel guilty, I was thinking of ()
and [] as being calls to constructors which returned shiny new tuple and/or
list objects (with the contents being arguments to those constructors).
I've learned a lot since then; now I know that the list gnomes and the tuple
fairies sneak in and replace the bracket characters with billows of cotton
candy. Problems arise when the cotton candy is soaked by over optimisation
by the evil language wizards, though I discovered that the resulting
solution is quite tasty when carbonated.
In some weird way, I like the is statement. It appears in thousands of
places throughout my code. I check object identity far more often than
object equivalence, as many of my libraries, in order to do a decent
equality check might have to do a recursive search through thousands of
nodes (and since they can have references to their parents, the equality
becomes quite ugly). Still, carbonation makes it all quite palatable.
Just because something is explicitly forbidden, goes against all laws of
nature, offends half the population, destroys one's life and family, and
casts one into the deepest pits of Tartarus doesn't necessarily mean that
thing should be avoided...
Or so I tell myself...
Mike
PS: Pointing out that it's in a document with the official disclaimer: "for
language lawyers" , is like pointing out ''There's no point in acting all
surprised about it. All the planning charts and demolition orders have been
on display in your local planning department on Alpha Centauri for fifty of
your Earth years, so you've had plenty of time to lodge any formal complaint
and it's far too late to start making a fuss about it now.'' ;)
-----Original Message-----
From: Tim Peters [mailto:tim.one at home.com]
Sent: Wednesday, April 18, 2001 03:51
To: Python List (E-mail)
Subject: RE: Idiom gone, or did it really ever exist? () is ()
...
It has never worked by design. It stopped working by accident when Guido
added empty-tuple caching in revision 2.9 of tupleobject.c. He did that in
October of 1993. Have you been in a time warp <wink>?
Any code relying on unique object identity for literals of any object of any
immutable type is simply wrong. The language doesn't guarantee anything
here, and the implementation can & does vary across releases, or even
bugfixes. The Reference Manual has always said (section "Objects, values
and
types"):
...
I don't know what accounts for this. Do users not understand how object
identity works in Python, or are they so fanatically devoted to tricks that
they're willing to chance it despite knowing it isn't safe? 'Fess up, Mike:
my bet is that when you *started* using this trick, you knew you were
cheating.
...
More generally, people using "is" without knowing what they're doing should
simply stop using it, tuples or not. How to tell if you're one of them: if
when you use "is", you feel a twinge of pride in being clever <0.5 wink>.
Safe (intended, documented and supported) uses for "is" are dull as dog
food.
...
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