Python identity: Multiple personality disorder, need code shrink [duplicate]

Question

Possible Duplicate:
Python “is” operator behaves unexpectedly with integers

I stumbled upon the following Python weirdity:

>>> two = 2
>>> ii = 2

>>> id(two) == id(ii)
True
>>> [id(i) for i in [42,42,42,42]]
[10084276, 10084276, 10084276, 10084276]

>>> help(id)
Help on built-in function id in module __builtin__:

id(...)
    id(object) -> integer

    Return the identity of an object.  This is guaranteed to be unique among
    simultaneously existing objects.  (Hint: it's the object's memory address.)

1. Is every number a unique object?
2. Are different variables holding the same elemental values (for example, two,ii) the same object?
3. How is the id of a number generated by Python?
4. In the above example, are two and ii pointers to a memory cell holding the value 2? That would be extremely weird.

Help me untangle this identity crisis.

Some more weirdities:

>>> a,b=id(0),id(1)
>>> for i in range(2,1000):
   a,b=b,id(i)
   if abs(a-b) != 12:
    print('%i:%i -> %i' % (i,a,b))

The above code examines if ids of consecutive integers are also consecutive, and prints out anomalies:

77:10083868 -> 10085840
159:10084868 -> 10086840
241:10085868 -> 10087840
257:10087660 -> 11689620
258:11689620 -> 11689512
259:11689512 -> 11689692
260:11689692 -> 11689548
261:11689548 -> 11689644
262:11689644 -> 11689572
263:11689572 -> 11689536
264:11689536 -> 11689560
265:11689560 -> 11689596
266:11689596 -> 11689656
267:11689656 -> 11689608
268:11689608 -> 11689500
331:11688756 -> 13807288
413:13806316 -> 13814224
495:13813252 -> 13815224
577:13814252 -> 13816224
659:13815252 -> 13817224
741:13816252 -> 13818224
823:13817252 -> 13819224
905:13818252 -> 13820224
987:13819252 -> 13821224

Note that a pattern emerges from 413 onwards. Maybe it's due to some voodoo accounting at the beginning of each new memory page.

Answer 1

Integers between -1 and 255(?), as well as string literals, are interned. Each instance in the source actually represents the same object.

In CPython, the result of id() is the address in the process space of the PyObject.