amazon-braket
Bug: Chained Observables should not be allowed
Describe the bug Observables should not be chained together.
In the Amazon Braket SDK, Observable.I() and Observable.X() are used to create identity and Pauli-X observables, respectively. However, these are not methods that are typically chained together. Each of these calls is intended to create a separate observable object, and chaining them like Observable.I().X() suggests applying one after the other, which doesn't align with how observables are used in the SDK.
To reproduce The following code snippet should not be valid.
from braket.circuits import Observable
Observable.I().X()
This is a side effect of each observable being registered to Observable:
https://github.com/amazon-braket/amazon-braket-sdk-python/blob/0370766feca0be3a5a3128b44f65cf5132ca1099/src/braket/circuits/observables.py#L73
Since they're registered as class methods, they can also be called on any instance of Observable; unfortunately, I don't think there's a simple way to restrict instances from calling the class method. Ideally, we would get rid of the registrations altogether, but that would be a pretty far-reaching breaking change.
