Backward compatibility¶

To reduce the risk of failure, changing the C API should be as much as possible compatible with the old C API (Python 3.7 C API). One solution for that is to provide a backward compatible header file and/or library.

Backward compatibility with Python 3.7 and older¶

For example, if PyDict_GetItem() is removed because it returns a borrowed reference, a new function PyDict_GetItemRef() which increases the reference counter can be added in the new API. But to make it backward compatible, a macro can be used in Python 3.7 using PyDict_GetItem() and Py_XINCREF(). Pseudo-code:

static PyObject*
PyDict_GetItemRef(PyObject *dict, PyObject *key)
{
    PyObject *value = PyDict_GetItem(dict, key);
    Py_XINCREF(value);
    return value;
}

Option questions:

Should the backward compatibility layer be only a header file? Should it be a C library?
Should we support Python 2.7? Technically, supporting Python 2 shouldn’t be hard since the many functions of the C API are the same between Python 2 and Python 3.

Forward compatibility with Python 3.8 and newer¶

C extensions have to be modified to become compatible with the new C API, because of removed functions for example.

Open question: support Python 2?¶

Would it be possible to provide a basic support of Python 2 in the new C API?

Open question: how to install the compatibility layers¶

pip install something?

Backward compatibility¶