Constant integer Attributes in Python Module written in C

Question

I implemented a python extension module in C according to https://docs.python.org/3.3/extending/extending.html

Now I want to have integer constants in that module, so I did:

module= PyModule_Create(&myModuleDef);
...
PyModule_AddIntConstant(module, "VAR1",1);
PyModule_AddIntConstant(module, "VAR2",2);
...
return module;

This works. But I can modify the "constants" from python, like

import myModule
myModule.VAR1 = 10

I tried to overload __setattr__, but this function is not called upon assignment.

Is there a solution?

StoryTeller - Unslander Monica · Accepted Answer · 2017-02-23 06:21:58Z

6

You can't define module level "constants" in Python as you would in C(++). The Python way is to expect everyone to behave like responsible adults. If something is in all caps with underscores (like PEP 8 dictates), you shouldn't change it.

edited Feb 23, 2017 at 6:21

answered Feb 22, 2017 at 14:23

StoryTeller - Unslander Monica

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4 Comments

too honest for this site Over a year ago

C does not support symbolic constants of arbitrary type. It is not C++. Only enum-constants are possible, but those are always int. And in Python, you could change the setter for an object. But normally one avoids the effort and relies on the convention.

StoryTeller - Unslander Monica Over a year ago

@Olaf - True, but in this case the OP is trying to prevent a reference from rebinding, which isn't possible in Python at all. And since Python integers are all immutable objects, __setattr__ is immaterial.

too honest for this site Over a year ago

Yes, that would require a "normal" class with all the overhead involved. That's why I agree about relying on the convention (if that was not clear from my comment).

Antti Haapala Over a year ago

It is indeed possible, if the module is replaced with an instance of custom class, but yeah, I wouldn't do it either. Also, import math; math.PI = 3

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