Understanding Enum Behavior in Python: Why Inherited Properties Can Behave Similarly

Learn why inherited properties from `abc.ABC` show the same value in Python's `Enum` when not defined correctly, and how to fix this issue.
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This video is based on the question https://stackoverflow.com/q/68125178/ asked by the user 'jett chen' ( https://stackoverflow.com/u/7295169/ ) and on the answer https://stackoverflow.com/a/68125333/ provided by the user 'juanpa.arrivillaga' ( https://stackoverflow.com/u/5014455/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Enum Behavior in Python: Why Inherited Properties Can Behave Similarly

When working with classes in Python, particularly when using Enum and abc.ABCMeta, developers may encounter perplexing issues. One common situation involves creating multiple service classes that seem to inherit the same property value, leading to confusion. If you've found yourself in this predicament while using Python 3.8, you’re not alone. Let’s delve into this problem and uncover the solution.

The Problem

You are trying to create two different services — ForwarderService and LogService. Upon inheriting from an abstract class, both services appear to return the same property value instead of distinctly identifying themselves. Here’s a simpler breakdown of your issue:

You have defined a base class Service using abc.ABCMeta, which includes an abstract property called type.

You have implemented this property in your ForwarderService and LogService classes to return different values from the ServiceType enum.

However, when you run your code, both calls to s1.type and s2.type return the same enum value.

Your Code Example

[[See Video to Reveal this Text or Code Snippet]]

The Root Cause: A Typo in Enum Definition

The confusion stems from how the Enum is defined. In your ServiceType enum declaration, you used this line:

[[See Video to Reveal this Text or Code Snippet]]

The auto function generates a number automatically for each enum member. However, in your case, it lacks parentheses, causing both Forwarder and Log entries to share the same value.

Correcting the Enum

To ensure that both services return distinct values, modify your enum definition as follows:

[[See Video to Reveal this Text or Code Snippet]]

Now, when you implement the type property for both services, they will return different enum values as you intended.

Example Output After Fixing the Code

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By simply adding parentheses to the auto() function in your Enum class definition, you can resolve the issue of both services returning the same value. This highlights the necessity for developers to be meticulous with function calls in Python. Small mistakes can lead to confusing behaviors in object-oriented programming, especially when abstract classes and enums are involved.

Understanding how to correctly utilize the enum functionality ensures that your service classes behave as expected. With this information, you can tackle similar issues in your code or even enhance your understanding of Python's inheritance and enumeration capabilities.

Happy coding!

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