Can I append gates in a certain position in a Qiskit circuit

Question

I have a question regarding modifying Qiskit circuits. I have a set of circuits that are pretty similar to each other. The only difference being some gates in the beginning of each circuit. I was wondering if instead of creating new circuits each time, I could just append gates to the beginning of the circuit. However, currently, all the methods I am aware of that act on the QuantumCircuit only append to the end of the circuit.

Is there a way I can add certain gates to the beginning of a Qiskit Circuit as opposed to creating new ones each time?

Answer 1

Have a look at Introduction to Coding Quantum Algorithms: A Tutorial Series Using Qiskit.

In lesson 2, there is a lot of statements allow you manipulate circuits. You can add a gate on specific place, delete a gate, combine circuits etc.

The manual I refer to is very easy to understand. Each manipulation is documented with examples.

Concerning combining of the circuit, you can use this statement:

newCircuit = oldCircuit1 + oldCircuit2

or

newCircuit = oldCircuit2 + oldCircuit1

So, you can easily add one circuit to the end or the begin of another circuit.