Learning Python Design Patterns - Second Edition

Drawbacks of the Singleton pattern

While Singletons are used in multiple places to good effect, there can be a few gotchas with this pattern. As Singletons have a global point of access, the following issues can occur:

• Global variables can be changed by mistake at one place and, as the developer may think that they have remained unchanged, the variables get used elsewhere in the application.
• Multiple references may get created to the same object. As Singleton creates only one object, multiple references can get created at this point to the same object.
• All classes that are dependent on global variables get tightly coupled as a change to the global data by one class can inadvertently impact the other class.

Note

As part of this chapter, you learned ...