When is that useful? e.g. A velocity controller class of dual arm robots (x: arm index).

Implementation †

TMultiSingleton

Usage †

Define a class where this class is used as the meta class.

class X(object):
  __metaclass__= TMultiSingleton

In X.__init__, the first argument should be the mode value (x).

In a function of X, use X._delete(self.x) to delete the instance (or reduce the reference count).

X can be instantiated like a usual class:

x1,x2,x3= X(1),X(1),X(2)

where x1 and x2 are the same instance (ids are the same) since they have the same mode value (1). x3 is a different instance.

Reference †

• https://python-3-patterns-idioms-test.readthedocs.io/en/latest/Singleton.html
• https://kiwamiden.com/singleton-in-python
• http://www.denzow.me/entry/2018/01/28/171416