Python - Change value at memory address

Question

For example, I have a variable called a, and need to change it by its memory address:

a: str = "hello"
address: int = id(a)

change_by_address(address, a, 'newval') # is something like this possible?

Is there some way to do this, perhaps in the ctypes library?

How about globals()["a"] = "world"? Would that fit your needs? There is also a locals() version of that as well. — JonSG
– JonSG, Commented Mar 10, 2022 at 20:35
pedantically, id() is not guaranteed to be the memory address of the object, and this is an implementation detail of CPython (though this is almost always the case) — ti7
– ti7, Commented Mar 10, 2022 at 20:49
Yes, there is. I recently did it with ints and you can similarly do it with strings. But you shouldn't. Why do you think you need to? — Kelly Bundy
– Kelly Bundy, Commented Mar 10, 2022 at 20:57
Here's an answer where you can do this in CPython, and also demonstrates why you shouldn't. — Mark Tolonen
– Mark Tolonen, Commented Mar 10, 2022 at 21:34

MartinKondor · Accepted Answer · 2022-03-10 20:40:47Z

1

Well you can read by address in python:

import ctypes


a = 10
memfield = (ctypes.c_int).from_address(id(a))
print(memfield) # c_int(15)

But as far as I know, you cannot change values by address.

answered Mar 10, 2022 at 20:40

MartinKondor

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Comments

Tim Roberts · Accepted Answer · 2022-03-10 20:32:53Z

0

Absolutely, positively not. That ID is an address of SOMETHING in memory, but in C terms these are all moderately complicated data structures.

Python is not C. You cannot think of things in the same way.

answered Mar 10, 2022 at 20:32

Tim Roberts

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At least in CPython, you can do it, but corrupting what is in the OP's case an immutable str is definitely a bad idea.