Python and unsigned int

Question

Hi

I understand python does bit have data types strictly but I am in need of unsigned int

Let me brief you about the story. I have a c++ api which takes unsigned int as an argument and updates that value.

I have swig binding generated for this api which I will use into python.

Now, as we have option of below:
obj = myclass()

Makes obj as myclass instance, how to do it for unsigned int

Basically I want to declare a variable of unsigned int and laaa that variable to my api which will update value of unsigned int. Basically, I need a mechanism in python to generate unsigned int object

Answer 1

Though I am unfamiliar with using SWIG, I explored your question with ChatGPT. The primary answer was that it should work as long as you don't try to pass a negative integer.

Taking it further, I asked how to make SWIG cast a negative int as unsigned. It gave me the SWIG setup below. I hope this helps:

%module example
%{
#include "example.h"
%}

// Custom typemap to convert negative Python integers to their unsigned representation
%typemap(in) unsigned int {
long temp = PyLong_AsLong($input);
if (PyErr_Occurred()) return NULL; // Handle conversion errors

$1 = static_cast<unsigned int>(temp); // Proper bitwise conversion
}

%include "example.h"

Answer 2

have you tried ctypes?

import ctypes

u32_1 = ctypes.c_uint32(-1).value
print(u32_1)

u8_1 = ctypes.c_uint8(0).value
print(u8_1)

u8_2 = ctypes.c_uint8(-1).value
print(u8_2)

https://docs.python.org/3/library/ctypes.html

Answer 3

Ketan Lalcheta
perhaps go over the swig documentaion once again. specifially in the typemap section. Brian's example uses this.

31.8.1 What is a typemap?

https://www.swig.org/Doc1.3/JUMP_LINK__&&__Python__&&__JUMP_LINK.html#Python_nn2

also, why choose Swig and not Cython? Swig is harder to work with because it's designed for multiple languages. Cython is for Python specifically.

Answer 4

Bob_Li tried with ctypes, but no success

Not sure about Cython as I never heard or used it.

Even though I am not in a position to use cython inplace of swig, it will be a good point got me to get overview of it. Thanks for bringing this up.

Answer 5

Thanks Brian

I was also only concerned about non negative values only.

I just assigned as below:
a = 0

And expected it to work , but it did not. type(a) is int and as python does not have strong type for unsigned int may be the reason.

This made me think about what would happen if I have two api as below in C++.

void display(int a);
void display(unsigned int);

Will above work with swig for python ? If it does not work, what to do.

If it works and generate binding of python then

a = 3
display(a) will call unsigned int or int version?

Answer 6

Hi

Answer 7

I started from below