Python Programming with Design Patterns

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The Singleton Pattern

The Singleton pattern is grouped with the other creational patterns, although, to some extent, it is a “noncreational” pattern. There are any number of cases in programming where you need to make sure that there can be one, and only one, instance of a class. For example, your system can have only one window manager or print spooler, as well as a single point of access to a database engine.

Python does not directly have a feature where a single static variable will be accessible from all class instances, so a simple flag won’t work. Instead, this technique utilizes two subtle Python features you might not be aware of: the static method and the __instance variable.

Python has a Decorator that tells the compiler to make ...