# Protocols This module provides the protocols used throughout the package. A [`typing.Protocol`](https://docs.python.org/3/library/typing.html#typing.Protocol) is an interface that a class can fulfill structurally, without explicitly inheriting from it. For example, any class that implements a `__len__` method satisfies [`Sized`](https://docs.python.org/3/library/typing.html#typing.Sized), whether or not it says so anywhere in its class hierarchy. The protocols here follow the same idea, each centered on a small set of dunder-style methods. A class implementing them thereby satisfies the protocol and becomes usable wherever it is expected, without any explicit registration. | Protocol | Methods | Helper functions | |------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [`SupportsCommutators`](../stubs/qiskit_bosons.protocols.SupportsCommutators.html.md#qiskit_bosons.protocols.SupportsCommutators) | `_commutator_`, `_anti_commutator_`, `_double_commutator_` | [`commutator()`](../stubs/qiskit_bosons.operators.library.commutator.html.md#qiskit_bosons.operators.library.commutator), [`anti_commutator()`](../stubs/qiskit_bosons.operators.library.anti_commutator.html.md#qiskit_bosons.operators.library.anti_commutator), [`double_commutator()`](../stubs/qiskit_bosons.operators.library.double_commutator.html.md#qiskit_bosons.operators.library.double_commutator) |