[Tutor] How memory works in Python

[Mats Wichmann]

On 1/7/20 7:44 AM, Deepak Dixit wrote:
> Hi Team,
> 
> I was thinking on the memory management in Python but little confused here
> because when I assign same value of type number and string to different
> variable, it points to same memory but when I do it for list or tuple it
> points to different memory locations.
> 
> Here is the code and the output:
> 
> # test.py
> x1 = 10
> y1 = 10
> 
> x2 = "Hello"
> y2 = "Hello"
> 
> x3 = [10]
> y3 = [10]
> 
> x4 = (10,)
> y4 = (10,)
> 
> print id(x1) == id(y1)
> print id(x2) == id(y2)
> print id(x3) == id(y3)
> print id(x4) == id(y4)
> 
> deepak at Deepak-PC:~$ python test.py
> True
> True
> False
> False
> 
> 
> Can you help me to understand how it works?


quite simply, if works as you expect, but with some optimizations. 
Turns out small integers are cached in CPython - they reuse the same 
object. The current range of that is something like up to 256 (I think a 
small number of negative integers also have this happen).  Try that 
experiment again with bigger numbers.

Similarly for strings, small strings are interned, try it with a 
considerably longer string.

You can cause the string interning to happen yourself with the intern 
function, see this example:

 >>> y1 = "Hello, this is a much longer string"
 >>> y2 = "Hello, this is a much longer string"
 >>> print(id(y1) == id(y2))
False
 >>> import sys
 >>> y1 = sys.intern("Hello, this is a much longer string")
 >>> y2 = sys.intern("Hello, this is a much longer string")
 >>> print(id(y1) == id(y2))
True
 >>>