Qiskit: Extract individual Pauli strings from a PauliSumOp

Question

Suppose I have a PauliSumOp as follows:

from qiskit.opflow import X, Z, I, Y

h = (X ^ X ^ I) + (I ^ Y ^ Y) + (Z ^ Z ^ X)

I would like to go over the Pauli strings and do something with each string (for example, I need to know the positions of nontrivial Pauli matrices, but that's beside the point). I can iterate over h:

for k in h:
    ...

In this case, k will be a PauliSumOp with one Pauli string and one weight. The trouble is, I can't understand how to get the string itself (for example as a str, but a PauliOp will also do).

Is there a recommended way to extract individual Pauli strings from a PauliSumOp?

Answer 1

You can convert PauliSumOp into PauliOp with to_pauli_op.

from qiskit.opflow import X, Z, I, Y

h = (X ^ X ^ I) + (I ^ Y ^ Y) + (Z ^ Z ^ X)
for k in h.to_pauli_op():
    print(k)

XXI
IYY
ZZX