I’ve led the maintenance and development of a medium sized (100s of kloc) Python codebase over a period of five years. As it matured, the code became significan

I’ve led the maintenance and development of a medium sized (100s of kloc) Python codebase over a period of five years. As it matured, the code became significantly less fragile and more maintainable. Using private members of modules (or any other object) turned into way less of a problem as we improved our design. Turns out the problems were mostly around I/O and mutable state. We fixed those problems by pushing side effects and mutation as far out to the edge of the codebase as possible. If your core data processing routines don’t have side effects and don’t mutate global state, who cares who the caller is?