Data Model

Container Protocols

Container methods connect objects to indexing, membership, and item assignment.

__setitem__ gives assignment syntax to a custom container.

Source

class Scores:
    def __init__(self):
        self._scores = {}

    def __setitem__(self, name, score):
        self._scores[name] = score

scores = Scores()
scores["Ada"] = 98
print(scores._scores)

Output

{'Ada': 98}

__contains__ answers membership tests written with in.

Source

class Scores:
    def __init__(self):
        self._scores = {"Ada": 98}

    def __contains__(self, name):
        return name in self._scores

scores = Scores()
print("Ada" in scores)

Output

True

__getitem__ connects bracket lookup to your internal storage.

Source

class Scores:
    def __init__(self):
        self._scores = {"Ada": 98}

    def __getitem__(self, name):
        return self._scores[name]

scores = Scores()
print(scores["Ada"])

Output

Notes

Implement the narrowest container protocol your object needs.
Use KeyError and IndexError consistently with built-in containers.
If a plain dict or list is enough, prefer it over a custom container.

Run the complete example

Expected output

True
98

Execution time appears here after you run the example.

Container Protocols

See also

Run the complete example

Example code

Expected output