Singleton pattern

singleton

Provides a meta class to ensure single instantiation.

class DMT.core.singleton.Singleton

Bases: type

Implements the Singleton design pattern. Classes that use this class as a metaclass can only be initiated once.

If a new object of a singleton class is created, the already existing one is returned. Source: https://stackoverflow.com/questions/6760685/creating-a-singleton-in-python

Here something else is added: If a already existing object is “created” again, it tries to transfer the given kwargs to the old object.

Examples

The simulation controller should only exist once because of possible blocking of resources. This class is used to see singleton in action:

>>> sim_con1 = SimCon(n_core=4)
>>> sim_con1.n_core
4

If now a second simulation controller is created:

>>> sim_con2 = SimCon(n_core=8)
>>> sim_con2.n_core
8

The new attribute is overwritten with the new value. As the change is made to the already existing instance, this also has now 8 cores:

>>> sim_con1.n_core
8