Terry Reedy a écrit :
Mel wrote:
castironpi wrote:
It would be nice to put together a really canonical case of the use of
the 'is' comparison. FTSOA for the sake of argument, when do you use
it? Why is it even in the language?
My poster child use case is in a MUDD game. For instance, the player
represented by `this_player` has picked up the yoghurt. We notify the
other players using code that boils down to:
for person in this_room.inhabitants:
if person is not this_player:
person.notify ('%s has picked up the %s.'
% (this_player.name, 'yoghurt'))
The `is` test avoids telling this_player something he already knows.
Perhaps the code could be written to make an equality test work, but then
again, perhaps the game could have a much more interesting use for
equality
between persons.
Excellent example. There are three
make it four.
uses for 'is'.
1. Minor optimization of comparison with None, True, False.
Warning (to any python newbie reading this): x is True is *very*
different from x == True. IOW ;: don't use 'is' with True and False
unless you know *exactly* what you're doing.
2. Testing the implementation: 'a=1;b=1;a is b' *should* be True, while
'a=257;b=257;a is b' *should* be False. The CPython test suite has
tests like this.
3. Comparision of user class objects where identify is important.
Objects representing people is certainly such a case ;-).
4. Anywhere you want to test identity.
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