Python getter → What Is __getitem__?

__getitem__ is a method in Python that is called when an object is indexed (obj[key]) or sliced (obj[start:stop]). Defining this method inside a class allows instances of that class to be used like lists or dictionaries.

📌 Basic Usage

class MyList:
    def __init__(self, data):
        self.data = data

    def __getitem__(self, index):
        print(f"Called with index: {index}")
        return self.data[index]

my_list = MyList([10, 20, 30])
print(my_list[1])  # => Called with index: 1
                   # => 20

🎯 Key Features

• When obj[key] is called, obj.__getitem__(key) is called automatically.
• key can be not only an integer, but also a slice, tuple, string, and more.

✅ Slicing Can Also Be Supported

class MyList:
    def __init__(self, data):
        self.data = data

    def __getitem__(self, index):
        print(f"Index received: {index}")
        return self.data[index]

lst = MyList([1, 2, 3, 4, 5])
print(lst[1:4])  # 슬라이스 객체(slice(1,4,None))가 전달됨

📦 Example: Mimicking a Two-Dimensional Array

class Matrix:
    def __init__(self, rows):
        self.rows = rows

    def __getitem__(self, index):
        return self.rows[index]

m = Matrix([[1, 2], [3, 4]])
print(m[0][1])  # 2

⚠️ Notes

• __getitem__ is read-only. To support writing, you need to define __setitem__.
• It is a good idea to handle KeyError, IndexError, and other exceptions appropriately.

If you’re curious, I can also explain __setitem__ and __delitem__. Would you like to learn more?