how python variable works?

Question

How variables work in python? I tried understand it by assigning a value to a variable(a) and checking memory address of it.But,when I changed the value of that variable(a),I got another memory address.what is the reason for that? and that memory address is in the stack area of the memory? and the scope of it?,when I call del a,only variable identifier('a') was deleted.but,It is still on the memory.After,I call id(3),then,that memory address in the code section of the memory?and how python variables stored in memory?,anyone can explain more?

Code:

#!/usr/bin/python3
import _ctypes
a=45
s=id(a)
print(s)
a=a+2
d=id(a)
print(d)
print(_ctypes.PyObj_FromPtr(s))
del a
print(_ctypes.PyObj_FromPtr(d))
print(id(3))

Output:

10915904
10915968
45
47
10914560

Answer 1

What you're seeing is an optimization detail of CPython (the most common Python implementation, and the one you get if you download the language from python.org).

Since small integers are used so frequently, CPython always stores the numbers -5 through 256 in memory, and uses those stored integer objects whenever those numbers come up. This means that all instances of, say, 5 will have the same memory address.

>>> a = 5
>>> b = 5
>>> id(a) == id(b)
True
>>> c = 4
>>> id(a) == id(c)
False
>>> c += 1
>>> id(a) == id(c)
True

This won't be true for other integers or non-integer values, which are only created when needed:

>>> a = 300
>>> b = 300
>>> id(a) == id(b)
False