Update the type hints for QuantumCircuit.append

[alexanderivrii]

The QuantumCircuit.append method looks as follows

    def append(
        self,
        instruction: Operation | CircuitInstruction,
        qargs: Sequence[QubitSpecifier] | None = None,
        cargs: Sequence[ClbitSpecifier] | None = None,
        *,
        copy: bool = True,
    ) -> InstructionSet:

with the instruction being appended to a quantum circuit being of type Operation | CircuitInstruction.

In practice, however, we can add also anything that has a to_instruction method (see also this comment). It would be nice to reflect this functionality in the type hints and/or in the following docstring.

[Ak-ash22]

Hello... looks like this is issue is still free for grabs. May I take this up?

[alexanderivrii]

Thank you! You are now assigned to the task.

[Ak-ash22]

Hello @alexanderivrii , I am thinking of modifying things the following way:

1. type hints from instruction: Operation | CircuitInstruction to instruction: InstructionLike
2. and docstring to include additionally in the , :class: ~.circuit would be converted into .circuit.Instruction. and include in the Args::class with .to_instruction() attribute.

What do you suggest about this? If you have a better way of putting things, kindly let me know.

[Gyan-max]

Hi @Ak-ash22 and @alexanderivrii,

I appreciate the approach of introducing InstructionLike for better type hinting in QuantumCircuit.append. It makes sense to support objects with a to_instruction() method explicitly.

A few thoughts:

Would it be beneficial to include Union[Operation, CircuitInstruction, HasToInstruction] instead of a new alias (InstructionLike)? This would keep things explicit while maintaining flexibility.
Updating the docstring to clarify that any object with a .to_instruction() method is accepted is a great idea. Maybe we can also add a small example in the documentation?
Let me know if I can assist in testing or reviewing the changes!