Avoid deepcopy in pulse parser (backport #9063)

qiskit/pulse/parser.py

@@ -169,7 +169,7 @@ def visit_Expression(self, node: ast.Expression) -> ast.Expression:
         Returns:
             Evaluated value.
         """
-        tmp_node = copy.deepcopy(node)
+        tmp_node = copy.copy(node)
         tmp_node.body = self.visit(tmp_node.body)
 
         return tmp_node
@@ -240,6 +240,7 @@ def visit_UnaryOp(self, node: ast.UnaryOp) -> Union[ast.UnaryOp, ast.Constant]:
         Returns:
             Evaluated value.
         """
+        node = copy.copy(node)
         node.operand = self.visit(node.operand)
         if isinstance(node.operand, (ast.Constant, ast.Num)):
             val = ast.Constant(n=self._match_ops(node.op, self._unary_ops, node.operand.n))
@@ -255,6 +256,7 @@ def visit_BinOp(self, node: ast.BinOp) -> Union[ast.BinOp, ast.Constant]:
         Returns:
             Evaluated value.
         """
+        node = copy.copy(node)
         node.left = self.visit(node.left)
         node.right = self.visit(node.right)
         if isinstance(node.left, (ast.Constant, ast.Num)) and isinstance(
@@ -280,6 +282,7 @@ def visit_Call(self, node: ast.Call) -> Union[ast.Call, ast.Constant]:
         """
         if not isinstance(node.func, ast.Name):
             raise PulseError("Unsafe expression is detected.")
+        node = copy.copy(node)
         node.args = [self.visit(arg) for arg in node.args]
         if all(isinstance(arg, (ast.Constant, ast.Num)) for arg in node.args):
             if node.func.id not in self._math_ops.keys():

releasenotes/notes/remove-pulse-deepcopy-9a19aa7f6452248b.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    The Pulse expression parser should no longer periodically hang when called
+    from Jupyter notebooks.  This is achieved by avoiding an internal ``deepycopy``
+    of a recursive object that seemed to be particularly difficult for the
+    memoization to evaluate.