Indexing feature in Class

To add indexing functionality (like obj[i]) to a Python class, you need to implement the __getitem__ method in your class. Optionally, you can also implement __setitem__ and __delitem__ to handle assignment and deletion of items.

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Read indexing

class MyList:
    def __init__(self, data):
        self.data = data  # Store the data in an internal list

    def __getitem__(self, index):
        return self.data[index]  # Use the internal list's indexing

# Example usage
obj = MyList([10, 20, 30, 40])
print(obj[1])  # Outputs: 20

---

Write indexing

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

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

    def __setitem__(self, index, value):
        self.data[index] = value  # Allow modification of the internal list

# Example usage
obj = MyList([10, 20, 30, 40])
print(obj[1])  # Outputs: 20
obj[1] = 99    # Updates the second element
print(obj[1])  # Outputs: 99

---

Deletion at index

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

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

    def __setitem__(self, index, value):
        self.data[index] = value

    def __delitem__(self, index):
        del self.data[index]  # Remove the specified element

# Example usage
obj = MyList([10, 20, 30, 40])
print(obj[1])  # Outputs: 20
del obj[1]     # Deletes the second element
print(obj.data)  # Outputs: [10, 30, 40]

---

Support for Slicing

if isinstance(index, slice):
    ...

If you want your class to support slicing (e.g., obj[1:3]), you can handle this in the __getitem__, __setitem__, and __delitem__ methods by checking if the index is a slice.

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

    def __getitem__(self, index):
        if isinstance(index, slice):
            print("index is a slice", index)
        return self.data[index]  # Handles both single index and slicing

    def __setitem__(self, index, value):
        self.data[index] = value  # Handles both single index and slicing

    def __delitem__(self, index):
        del self.data[index]  # Handles both single index and slicing

# Example usage
obj = MyList([10, 20, 30, 40, 50])
print(obj[1:4])  # Outputs: [20, 30, 40]
obj[1:3] = [99, 100]  # Updates a slice
print(obj.data)  # Outputs: [10, 99, 100, 40, 50]

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Summary

1. Implement __getitem__ for read-only access (obj[i]).
2. Implement __setitem__ for assignment (obj[i] = value).
3. Implement __delitem__ for deletion (del obj[i]).
4. Handle slicing by leveraging the fact that index can be a slice object.