On 4/26/2012 2:01, Steven D'Aprano wrote:
On Wed, 25 Apr 2012 13:49:24 -0700, Adam Skutt wrote:
Though, maybe it's better to use a different keyword than 'is' though,
due to the plain English
connotations of the term; I like 'sameobj' personally, for whatever
little it matters. Really, I think taking away the 'is' operator
altogether is better, so the only way to test identity is:
id(x) == id(y)
Four reasons why that's a bad idea:
1) The "is" operator is fast, because it can be implemented directly by
the interpreter as a simple pointer comparison (or equivalent). The id()
idiom is slow, because it involves two global lookups and an equality
comparison. Inside a tight loop, that can make a big difference in speed.
2) The "is" operator always has the exact same semantics and cannot be
overridden. The id() function can be monkey-patched.
3) The "is" idiom semantics is direct: "a is b" directly tests the thing
you want to test, namely whether a is b. The id() idiom is indirect:
"id(a) == id(b)" only indirectly tests whether a is b.
4) The id() idiom already breaks if you replace names a, b with
expressions:
id([1,2]) == id([3,4])
True
You forgot one:
5) It would be a pain to write (and read)
if id(my_obj) == id(None)
and so anyone would come up with his/her own same_as(),
identical_to(), same_inst() and so on...
Kiuhnm
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