Clean Code in Python

Singleton and shared state (monostate)

The singleton pattern, on the other hand, is something not entirely abstracted away by Python. The truth is that most of the time, this pattern is either not really needed or is a bad choice. There are a lot of problems with singletons (after all, they are, in fact, a form of global variables for object-oriented software, and as such, are a bad practice). They are hard to unit test, the fact that they might be modified at any time by any object makes them hard to predict, and their side-effects can be really problematic.

As a general principle, we should avoid using singletons as much as possible. If in some extreme case, they are required, the easiest way of achieving this in Python is by using a module. ...