What is the purpose of __len__ in a Python class?

All Questions From This Chapter

__len__ in a Python class?

The purpose of __len__ in a Python class is to define how the built-in len() function should behave when called on an instance of that class.

Why it's used:

• When you implement __len__, you're telling Python how to compute the "length" of your custom object.

Example:

python
class MyCollection:
    def __init__(self, items):
        self.items = items

    def __len__(self):
        return len(self.items)

c = MyCollection([1, 2, 3])
print(len(c))  # Output: 3

Key Points:

• __len__ must return an integer ≥ 0.

• If __len__ is not defined, calling len() on the object will raise a TypeError.

It’s especially useful when creating custom container types that conceptually hold multiple items.

Tags: Python,Interview Preparation,Technology,