add dtype parameter to PauliSumOp.from_list (#8896)

* add dtype parameter to PauliSumOp.to_list

* add release note

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/opflow/primitive_ops/pauli_sum_op.py

@@ -431,19 +431,22 @@ def to_spmatrix(self) -> spmatrix:
     @classmethod
     def from_list(
         cls,
-        pauli_list: List[Tuple[str, complex]],
+        pauli_list: List[Tuple[str, Union[complex, ParameterExpression]]],
         coeff: Union[complex, ParameterExpression] = 1.0,
+        dtype: type = complex,
     ) -> "PauliSumOp":
         """Construct from a pauli_list with the form [(pauli_str, coeffs)]
 
         Args:
             pauli_list: A list of Tuple of pauli_str and coefficient.
             coeff: A coefficient multiplying the primitive.
+            dtype: The dtype to use to construct the internal SparsePauliOp.
+                Defaults to ``complex``.
 
         Returns:
             The PauliSumOp constructed from the pauli_list.
         """
-        return cls(SparsePauliOp.from_list(pauli_list), coeff=coeff)
+        return cls(SparsePauliOp.from_list(pauli_list, dtype=dtype), coeff=coeff)
 
     def is_zero(self) -> bool:
         """

releasenotes/notes/pauli-sum-op-dtype-cd09b4c6521aeb42.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Added ``dtype`` argument to :meth:`~.PauliSumOp.from_list`
+    for passing type information to the internal
+    :class:`~.SparsePauliOp`.

test/python/opflow/test_pauli_sum_op.py

@@ -305,6 +305,13 @@ def test_from_list(self):
         )
         self.assertEqual(target, expected)
 
+        a = Parameter("a")
+        target = PauliSumOp.from_list([("X", 0.5 * a), ("Y", -0.5j * a)], dtype=object)
+        expected = PauliSumOp(
+            SparsePauliOp.from_list([("X", 0.5 * a), ("Y", -0.5j * a)], dtype=object)
+        )
+        self.assertEqual(target.primitive, expected.primitive)
+
     def test_matrix_iter(self):
         """Test PauliSumOp dense matrix_iter method."""
         labels = ["III", "IXI", "IYY", "YIZ", "XYZ", "III"]