r wrote:
On Mar 11, 3:40 pm, Craig Allen <callen...@gmail.com> wrote:
On Mar 10, 1:39 pm, Paul Rubin <http://phr...@nospam.invalid> wrote:
Identical strings don't necessarily have the same id:
A more verbose way to put this is "Requesting a string with a value that
is the same an an existing string does not necessarily result in reuse
of the existing string but mey result in creation of a new, duplicate
string.
>>> a = "a"*1000
>>> b = "a"*1000
>>> id(a),id(b)
(137143648, 137144680)
>>> a==b
True
interesting, I thought they were supposed to.
Reuse of immutable objects is entirely up to the implementation.
CPython reuses small ints and identifier-like strings that it 'expects'
would otherwise be duplicated. There is no reason to expect that
the programmer will ask for 'a'*1000 again instead of explicitly reusing
the existing object. On the other hand, identifiers are almost always
reused, often multiple times.. (Non-reuse may even by a bug!.)
Are you joking? two objects == two ids. if not i would dump Python
forever!
Me too, but see rewording.
Do you think Vector(0,0,0) and Vector(0,0,0) would have the same id?
If the instances of Vector are immutable, possibly yes.
If Vector(0,0,0) were typically called hundreds of times within a
program, it might be worthwhile for the Vector class to pre-allocate one
instance with that value and return it for each of the hundreds of
calls. That would be an implementation decision, which could be changed
with experience.
Similarly, if one is populating a LARGE structure with duplicate values,
it may be worthwhile to cache values that are not cached by the interpreter.
Terry Jan Reedy
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