I'd change the title of this bpo item to "Prepare for removing the whcar_t caching in the Unicode C API". Note that the wchar_t caching was put in place to allow for external applications and C code to easily and efficiently interface with Python. By removing it you will slow down such code significantly, esp. on Linux and Windows where wchar_t code is fairly common (one of the reasons we added UCS4 in Python was to make the interaction with Linux wchar_t code more efficient). This should be clearly mentioned as part of the change and the compile time flags. BTW: You have a few other changes in the PR which don't have anything to do with the intended removal: - envsize = PySequence_Fast_GET_SIZE(keys); - if (PySequence_Fast_GET_SIZE(values) != envsize) { + envsize = PyList_GET_SIZE(keys); + if (PyList_GET_SIZE(values) != envsize) {