New submission from Christian Heimes <[email protected]>:
It's currently inconvenient and sometimes error-prone to initialize module
members in C. Even stdlib modules are sometimes missing error checks or have
reference counting issues in error path. I propose add three helpers to deal
with common cases:
1) declaration of simple attributes (int, str, bool, float) in an array of
structs
2) creation and addition of a new type from a type spec
3) creation and addition a new exception object
(1) Simple attribute declaration uses a NULL terminated array of
PyModuleConst_Def. The internal definition of the type can be hidden by macros.
Example:
static PyModuleConst_Def example_constants[] = {
PyModuleConst_None("none_value"),
PyModuleConst_Long("integer", 42),
PyModuleConst_Bool("false_value", 0),
PyModuleConst_Bool("true_value", 1),
PyModuleConst_String("somestring", "Hello"),
PyModuleConst_LongMacro(EXAMPLE_INT),
PyModuleConst_StringMacro(EXAMPLE_STRING),
{NULL},
}
A new function "int PyModule_AddConstants(PyObject *module, PyModuleConst_Def
*def)" populates the module object with attributes.
(2) Type initialization
The function "PyTypeObject * PyModule_AddNewTypeFromSpec(PyObject *module,
PyType_Spec *spec, PyObject *base)" is PyType_FromModuleAndSpec() +
PyModule_AddType(). Additionally to PyType_FromModuleAndSpec() it also handles
"base" argument with single type instance. The extra feature avoids
"PyTuple_Pack(1, baseclass)" in the caller. The function adds a strong
reference to the module object and returns a borrowed reference. The borrowed
reference is designed module state assignment.
(3) exception creation
The function "PyObject* PyModule_AddNewException(PyObject *module, const char
*name, const char *doc, PyObject *base, PyObject *dict)" creates a new
exception, calculates the attribute name for the qualified exception name, and
adds the exception to the module. It's PyErr_NewExceptionWithDoc() +
PyModule_AddObjectRef().
Note about (1): I first proposed to add PyModuleDef.m_constants, however we
cannot extend the struct easily becaues it conflicts with stable ABI. Petr
mentioned that he has plans to deal with the issue. Also see discussion
https://discuss.python.org/t/define-module-constants-in-pymoduledef/5749
----------
assignee: christian.heimes
components: C API
messages: 381144
nosy: christian.heimes
priority: normal
severity: normal
stage: patch review
status: open
title: Add helpers to populate modules in C
type: enhancement
versions: Python 3.10
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Python tracker <[email protected]>
<https://bugs.python.org/issue42376>
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