Unveiling the Secrets of Python 3.x's Magical Super()

Python 3.x introduces a peculiar aspect of the super() function: it can be invoked without arguments. This seemingly mundane behavior conceals a potent combination of compile-time magic and runtime support that provides immense flexibility and efficiency.

The Hidden Compile-Time Enchantment

To enable the argument-less super() call, the Python compiler performs an intricate maneuver during compilation. It creates a special class cell, which stores a reference to the class in which the super() call is defined. This cell ensures that super() can dynamically access the correct superclass at runtime, even if the class has been reassigned or decorated.

The Importance of Class Context

The reason why super() requires a reference to class is rooted in the concept of class context. In Python, methods are tightly bound to the class in which they are defined. When a method is called with super(), it needs to be able to identify the immediate superclass, which may differ from the current class due to inheritance or class decoration.

Unintended Consequences

The downside of relying on a class cell is its susceptibility to rebinding. If the super variable is reassigned to a different name, the class cell may not be able to find the correct superclass. This can lead to "RunTimeErrors: super(): class cell not found."

Practical Implications

This behavior can indeed pose threats to unsuspecting programmers. For instance, altering the class during runtime or using class decorators that rebind the class name can disrupt the normal functioning of super(). This is especially true for novice developers who may not fully grasp the relationship between class context and super().

Exceptions to the Rule

Super() is not the only feature in Python affected by rebinding issues. Some examples include class decorators that alter the class name, functions that rely on the module attribute, or methods that use the code attribute.

Maintaining Class Context

To avoid these pitfalls, it's essential to maintain the class context when using super() or other functions that depend on it. If the class context must be manipulated, explicitly pass the superclass or class as an argument to super(). This ensures that these functions will still function correctly, regardless of any rebinding or class alterations.

In conclusion, Python's magical super() implementation, facilitated by a compile-time class cell, provides convenient and efficient access to superclasses. However, understanding its reliance on class context and avoiding potential rebinding issues is crucial for harnessing its full potential safely.