Should I Use Class Attributes or Instance Attributes for Python Singletons?

When to Utilize Class Attributes for Singletons in Python

When creating Python classes with a single required instance, selecting the appropriate attribute strategy is crucial. Class attributes and instance attributes both offer unique advantages and disadvantages.

Class Attributes:

Class attributes are assigned directly to the class itself and are shared among all instances. This approach is suitable if all instances of the class require identical attributes. For example:

class MyController(Controller):
  path = "something/"
  children = [AController, BController]

Instance Attributes:

Instance attributes are associated with a specific instance of a class and are unique to that instance. They are created dynamically in the __init__() method. This approach is necessary when each instance requires unique values for its attributes. For example:

class MyController(Controller):
  def __init__(self):
    self.path = "something/"
    self.children = [AController, BController]

Which Approach for Singletons?

Since you have only one required instance of your class, it is recommended to use instance attributes in this scenario. Here are the reasons:

• Faster access: Instance attributes are accessed directly, without the need for an inheritance lookup from the class. This provides a slight performance advantage.
• No disadvantages: For a singleton class, there are no downsides to using instance attributes compared to class attributes.

Therefore, for your Python classes that require a single instance with shared configuration, it is more idiomatic and beneficial to define your attributes as instance variables.

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