guide-cleanup.rst

c

single: Cleanup

Cleanup – Dropping Support for Python 2

When users of your C extension are not using Python 2 any more, or you need to use one of Python 3's irresistible new features, you can convert the project to use Python 3 only. As mentioned earlier, it is usually not a good idea to do this until you have full support for both Pythons.

With py3c, dropping Python 2 basically amounts to expanding all its compat macros. In other words, remove the py3c.h header, and fix the compile errors.

• double: Cleanup; Strings double: Cleanup; Bytes double: Cleanup; Unicode

  Convert PyStr_* to PyUnicode_*; PyInt_* to PyLong_*.

• double: Cleanup; Module Initialization

  Instead of MODULE_INIT_FUNC(<name>), write:

  PyMODINIT_FUNC PyInit_<name>(void);
  PyMODINIT_FUNC PyInit_<name>(void)

• double: Cleanup; Types

  Remove Py_TPFLAGS_HAVE_WEAKREFS and Py_TPFLAGS_HAVE_ITER (py3c defines them as 0).

• double: Cleanup; Comparisons

  Replace PY3C_RICHCMP by its expansion, unless you keep the py3c/comparison.h header.

• Replace Py_RETURN_NOTIMPLEMENTED by its expansion, unless you either support Python 3.3+ only or keep the py3c/comparison.h header.
• Drop capsulethunk.h, if you're using it.
• Remove any code in #if !IS_PY3 blocks, and the ifs around #if IS_PY3 ones.

You will want to check the code as you're doing this. For example, replacing PyLong can easily result in code like if (PyInt_Check(o) || PyInt_Check(o)).

Enjoy your Python 3-compatible extension!