Use Custom Python Objects In A Boolean Context

In a boolean context, Python always evaluates the objects of a custom class to True. But this may not be desired in all cases. Here's how you can override this behavior.

The __𝐛𝐨𝐨𝐥__ dunder method is used to define the behavior of an object when used in a boolean context. As a result, you can specify explicit conditions to determine the truthiness of an object.

This allows you to use class objects in a more flexible and intuitive way.

As demonstrated above, without the __𝐛𝐨𝐨𝐥__ method (without_bool.py), the object evaluates to True. But implementing the __𝐛𝐨𝐨𝐥__ method lets us override this default behavior (with_bool.py).

Some additional good-to-know details

When we use ANY object (be it instantiated from a custom or an in-built class) in a boolean context, here’s what Python does:

First, Python checks for the __𝐛𝐨𝐨𝐥__ method in its class implementation. If found, it is invoked. If not, Python checks for the __𝐥𝐞𝐧__ method. If found, __𝐥𝐞𝐧__ is invoked. Otherwise, Python returns True.

This explains the default behavior of objects instantiated from a custom class. As the Cart class implemented neither the __𝐛𝐨𝐨𝐥__ method nor the __𝐥𝐞𝐧__ method, the cart object was evaluated to True.

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