How Can I Properly Handle Type Hints for Enclosed Classes in Python?

Handling Type Hints for Enclosed Classes in Python

Understanding the Issue

When defining a method that refers to the enclosing class as its return type, you may encounter an unresolved reference error. Let's consider the following code in Python 3:

This code fails with a NameError because the Position class is not defined within the scope of the __add__ method.

Resolving the Issue

Python 3.11 with 'Self' Type:

In Python 3.11 and later versions, you can use the Self type to reference the enclosing class within type hints:

Python 3.7 with '__future__ import annotations':

If you're using Python 3.7 or newer, you can enable the postponed evaluation of annotations by adding the following import statement:

With this enabled, the type hints will be stored as strings until the module is fully loaded, resolving the reference issue:

Python

For Python versions below 3.7, you can specify a string reference to the enclosing class using single quotes:

This creates a forward reference that will be resolved once the class is defined.

Additional Notes:

• If using dummy definitions or monkey-patching to add annotations, ensure that the annotations accurately reflect the class's type.
• In Python 3.10, the postponed evaluation of annotations was scheduled to become the default, but it has since been postponed to a future release.

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