On Tue, Jul 23, 2013 at 12:09 AM, Jim Mooney <cybervigila...@gmail.com>wrote:
> I've noticed that when I create a number of objects from a class, one
> after another, they're at different IDs, but the IDs all appear to be
> equidistant, so that they all appear to have the same size. But what does
> that size represent? is it bytes? ie - if I run this over and over I get
> different id numbers but they are always 40 apart. Or is that distance
> machine-specific as to units?:
>
>
> 41599624 - different results for each run but always 40 apart
> 41599664
> 41599704
> '''
>
When I saved your code as a file on my machine (Python 2.7 on Win8 64-bit)
and ran it from the command line, I got the same result as you - three IDs,
40 apart every time. However, I initially pasted your code into
PyScripter, and when I ran it inside PyScripter the results were different:
if the first ID was x, then the second was x+160, and the third was x+200.
(160 is obviously divisible by 40... I have no idea what conclusion to draw
from that.)
I simplified the test-harness portion as follows:
kronkList = []
for kronknum in xrange(0,100):
kronkList.append(Kronk(kronknum))
print(kronkList[kronknum].getzar())
print(kronkList[kronknum].getself())
and now the ID is incremented by 40 each time regardless how I run the
script.
Each time I run it, the last digit stays the same throughout the run (as
you would expect, given that we're adding 40 each time), but the last
digits are NOT consistent _between_ runs. It appears to always be an even
number, though.
As an experiment, I added a couple of extra methods and attributes to the
Kronk class, but it didn't change anything - IDs still incremented by 40
each time. eryksun will no doubt chime in to tell us exactly how object
IDs are derived in cPython, but I'll go out on a limb and say that they
have nothing to do with the size of the object; also that one would be very
silly to make a program rely in any way on predicting the next ID, since
external factors may throw off the calculations (as when I invoked your
original script from inside PyScripter). All that you can rely on is that
each unique object (i.e. doesn't pass an "is" comparison with any other
object) has a unique ID... and, for all I know, not even that.
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
