Getting pointer to the C extension module

[voidtrance]

I have a C extension which defines a class with various methods. In one of the class method, I need to get the __file__ attribute of the module. I know that I can use PyModule_GetFilenameObject() but I can’t figure out how to get a pointer to the module object. All I have is the pointer to the self instance object.

I’ve tried using PyType_GetModule(Py_TYPE(self)) or PyType_GetModuleByDef(Py_TYPE(self), &ModuleDef) but both return NULL.

How can I get a pointer to the module object without using a global variable?

[MegaIng (Cornelius Krupp)]

I don’t have exact experience with this post or the cpython api, but if you are defining a class method, shouldn’t self already be of the type, and calling Py_TYPE gives you type, i.e. the builtin root object?

Or are you defining an instance method and that was me misinterpreting your wording?

[MRAB (Matthew Barnett)]

Didn’t you call PyModule_Create or similar in the extension’s initialisation function? That returned a pointer to the module object.

[voidtrance]

@MegaIng

I don’t have exact experience with this post or the cpython api, but if you are defining a class method, shouldn’t self already be of the type, and calling Py_TYPE gives you type, i.e. the builtin root object?

Or are you defining an instance method and that was me misinterpreting your wording?

Yes, that was my understanding, which is why I used Py_TYPE(self) to get the type. However, that did not work.

[voidtrance]

@MRAB

Didn’t you call PyModule_Create or similar in the extension’s initialisation function? That returned a pointer to the module object.

I am. However, there are two things about that:

1. As far as I know, the __file__ attribute is only set after PyInit_*() returns so you can’t get the attribute value within PyInit_*().
2. Even if I could get the value, I would have to use a global variable to store the path, which I am trying to avoid. Otherwise, I could just use a global variable to store the pointer to the module.

[da-woods]

@voidtrance

As far as I know, the __file__ attribute is only set after PyInit_*() returns so you can’t get the attribute value within PyInit_*().

If you use multi-phase initialization then it’s available in the exec_module phase (which is usually the main one).

To use PyType_GetModule they need to be heap types (i.e. created by PyType_FromModuleAndSpec or similar).

Isolating Extension Modules — Python 3.12.4 documentation is a useful link (the "module state access from regular methods"section)

[voidtrance]

@da-woods

@voidtrance

As far as I know, the __file__ attribute is only set after PyInit_*() returns so you can’t get the attribute value within PyInit_*().

If you use multi-phase initialization then it’s available in the exec_module phase (which is usually the main one).

To use PyType_GetModule they need to be heap types (i.e. created by PyType_FromModuleAndSpec or similar).

Isolating Extension Modules — Python 3.12.4 documentation is a useful link (the "module state access from regular methods"section)

Your documentation link was very helpful. Thank you.

However, it seems that when attempting to access the module from a regular method through the defining class, the type still needs to be heap-allocated. In essence, it seems that, no matter what, multi-phase initializsation has to be used.

[voidtrance]

Switching to multi-phase initialization allowed me to successfully get the module pointer and the module path.

I still have to use a global variable since there is no way that I can store what I want in the class instance (I either have a pointer to the module or a pointer to the class but not both).