change the value of a variable in memory using python

Question

(In python) I want to be able to write something like a + b, and so that as a result a has the value of the sum of a and b, also so that id(a) does not change (that is, change data at the address of a variable in memory rather than create a new address with the result of the sum and refer to it with a).

My attempt to use += fails:

a, b = 5, 6
start_id = id(a)
a += b
print(start_id == id(a))
# Outputs: False

Try to run this: '' a = 5 b = 6 d = [] d += [id(a), id(b)] a += b d += [id(a)] print(d)'' — 0dminnimda, Mar 02 '20 at 13:56
I need the function result to be stored in the memory cell of variable a — 0dminnimda, Mar 02 '20 at 13:58
but this will not happen with regular functions in python (they put the result of the calculations in a new memory cell) — 0dminnimda, Mar 02 '20 at 13:59
Does this answer your question? [increment int object](https://stackoverflow.com/questions/1135335/increment-int-object) — Odysseus, Mar 02 '20 at 14:27
in the answers to the question "[increment int object](https://stackoverflow.com/questions/1135335/increment-int-object)" I did not find a clear answer to my question — 0dminnimda, Feb 24 '21 at 21:46

Xiidref · Answer 1 · 2020-03-03T13:33:36.900

In python pass reference only for objects. If you want do such a thing you need to create an object that represent your integer

You can also cheat a bit the system by taking the scope of the program when calling the function

def function(a,b, scope=locals()):
  var_name = [key for key, value in scope.items() if value == a][0]
  scope[var_name] += b


a = 4
b = 5
function(a, b)
print(a) #output 9

Note that here the result will be bound to the first variable with the same value of a which could be a big anoyement.

Odysseus · Answer 2 · 2020-03-02T14:27:03.813

want to make such an addition function (example of use: "a + b"), which will modify a and not return anything (In Python)

When doing this within a function you cannot simply use a += b because a would be treated as local variable which is not defined. Therefore you need to explicitly tell that you want to use the global variable a:

def add_to_a(val):
   global a
   a += val

a = 42
b = 1
add_to_a(b)

Since the actual question is now why id changes after changing the value of a the answer is: Because integres are immutable in python and you have to work around that - like in the answers in this question

change the value of a variable in memory using python

2 Answers2