Why Do Consecutive, Unnamed Python Class Instances Share the Same Object ID?

Same Object ID for Consequent Class Instances

When creating multiple instances of a class without assigning them a name, Python assigns the same ID to all of them. This behavior, which can be surprising at first glance, is due to the concept of object lifetimes in Python.

The ID of an object ensures its uniqueness only during the object's lifetime. In the example provided, someClass() is called multiple times within the scope of a single statement. Each call creates a new object. However, since these objects are not assigned to any variable and their scope ends immediately after the statement finishes executing, they become available for garbage collection.

In CPython, the default implementation of Python, garbage collection uses reference counting. Additionally, the ID of an object is tied to its memory location. This combination of factors explains why the consequent instances of someClass() share the same ID: memory gets deallocated and reused as new objects are created in the same function scope.

To address this behavior and ensure distinct IDs for class instances, consider either keeping the objects around in a data structure or implementing a custom ID scheme within the class.

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