Add a parameters method to the Operators (qiskit-community/qiskit-aqu…

…a#1194)

Co-authored-by: Manoel Marques <Manoel.Marques@ibm.com>
Co-authored-by: Steve Wood <40241007+woodsp-ibm@users.noreply.github.com>

qiskit/aqua/operators/list_ops/list_op.py

@@ -327,6 +327,15 @@ def __repr__(self) -> str:
                                                      self.coeff,
                                                      self.abelian)
 
+    @property
+    def parameters(self):
+        params = set()
+        for op in self.oplist:
+            params.update(op.parameters)
+        if isinstance(self.coeff, ParameterExpression):
+            params.update(self.coeff.parameters)
+        return params
+
     def assign_parameters(self, param_dict: dict) -> OperatorBase:
         param_value = self.coeff
         if isinstance(self.coeff, ParameterExpression):

qiskit/aqua/operators/operator_base.py

@@ -414,6 +414,13 @@ def tensorpower(self, other: int) -> Union['OperatorBase', int]:
         """
         raise NotImplementedError
 
+    @property
+    @abstractmethod
+    def parameters(self):
+        r""" Return a set of Parameter objects contained in the Operator.
+        """
+        raise NotImplementedError
+
     # Utility functions for parameter binding
 
     @abstractmethod

qiskit/aqua/operators/primitive_ops/primitive_op.py

@@ -217,6 +217,15 @@ def eval(self,
                           OperatorBase] = None) -> Union[OperatorBase, float, complex]:
         raise NotImplementedError
 
+    @property
+    def parameters(self):
+        params = set()
+        if isinstance(self.primitive, (OperatorBase, QuantumCircuit)):
+            params.update(self.primitive.parameters)
+        if isinstance(self.coeff, ParameterExpression):
+            params.update(self.coeff.parameters)
+        return params
+
     def assign_parameters(self, param_dict: dict) -> OperatorBase:
         param_value = self.coeff
         if isinstance(self.coeff, ParameterExpression):

qiskit/aqua/operators/state_fns/state_fn.py

@@ -292,6 +292,15 @@ def eval(self,
                           OperatorBase] = None) -> Union[OperatorBase, float, complex]:
         raise NotImplementedError
 
+    @property
+    def parameters(self):
+        params = set()
+        if isinstance(self.primitive, (OperatorBase, QuantumCircuit)):
+            params.update(self.primitive.parameters)
+        if isinstance(self.coeff, ParameterExpression):
+            params.update(self.coeff.parameters)
+        return params
+
     def assign_parameters(self, param_dict: dict) -> OperatorBase:
         param_value = self.coeff
         if isinstance(self.coeff, ParameterExpression):