I know that python has a concept of small integers which are numbers from -5
to 256
, and if two variables assign to same numbers between this range, they both will use the same underlying object.
From Python documentation,
#ifndef NSMALLPOSINTS
#define NSMALLPOSINTS 257
#endif
#ifndef NSMALLNEGINTS
#define NSMALLNEGINTS 5
#endif
/* Small integers are preallocated in this array so that they can
be shared. The integers that are preallocated are those in the
range -NSMALLNEGINTS (inclusive) to NSMALLPOSINTS (not inclusive).
*/
Also explained here,
The current implementation keeps an array of integer objects for all
integers between -5 and 256, when you create an int in that range you
actually just get back a reference to the existing object. So it
should be possible to change the value of 1. I suspect the behaviour
of Python in this case is undefined. :-)
Example,
a = 255
b = 255
print(id(a))
print(id(b))
gives the same id,
1561854394096
1561854394096
Which makes sense and also explained on this answer, "is" operator behaves unexpectedly with integers
If two numbers are less than -5
, they should also have different IDs as follows,
a = -6
b = -6
print(id(a))
print(id(b))
gives,
2827426032208
2827426032272
this makes sense so far,
But any number greater than 256
should have different id
,
This should return different IDs,
a = 257
b = 257
print(id(a))
print(id(b))
But it doesn't
2177675280112
2177675280112
Even when I am using very large integer, the IDs are same,
a = 2571299123876321621378
b = 2571299123876321621378
print(id(a))
print(id(b))
gives me,
1956826139184
1956826139184
Can someone tell me why number greater than 256 have same IDs even though in the Python code the range is -5
to 257
(not inclusive)
EDIT:
I have tried using PyCharm with both Python 2.7 and 3.6. Also tried on PythonTutor.com
See Question&Answers more detail:
os