This is partly a cleanup of the code. It also is preparation for getting the variables from the source (cross-platform) rather than from the symbols.
The change only touches the tool (and its tests).
The "Slot" helper (descriptor) is leaking references due to its caching mechanism. The change includes a partial fix to Slot, but also adds Variable.storage to replace the problematic use of Slot.
https://bugs.python.org/issue38187
Victor Stinner
Eric Snow
Pablo Galindo