It seems the approach that "The code for sysconfig.get_config_var() has a pretty clear intent: it will try to cast its return value to an int." has been accepted as true even though other parts of the code assumed the returned value was a string, and the CPython code was updated appropriately. This is causing problems for downstream libraries like NumPy, see https://github.com/numpy/numpy/pull/17906. If CPython does not wish to reconsider this decision, it should at least be documented clearly via a type hint and/or in the documentation for sysconfig.get_config_var https://docs.python.org/3/library/sysconfig.html#sysconfig.get_config_var