From c1afb9d47671c73a3870d3c767f24f425e5f42f0 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 27 May 2026 14:16:24 +0000
Subject: [PATCH] fix: preserve mediation confounders and no_directed_path in
 IdentifiedEstimand.__deepcopy__

The __deepcopy__ method of IdentifiedEstimand was missing three fields:
- mediation_first_stage_confounders
- mediation_second_stage_confounders
- no_directed_path

These are set during NDE/NIE identification. The bug caused them to be lost
when estimands are deep-copied (e.g. in refuters, TwoStageRegressionEstimator),
which could silently produce incorrect results in mediation analysis.

Adds two regression tests for the fixed behaviour.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
---
 .../causal_identifier/identified_estimand.py  |  3 ++
 .../test_auto_identifier.py                   | 32 +++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/dowhy/causal_identifier/identified_estimand.py b/dowhy/causal_identifier/identified_estimand.py
index 84bd1d8b67..b3873b72f7 100644
--- a/dowhy/causal_identifier/identified_estimand.py
+++ b/dowhy/causal_identifier/identified_estimand.py
@@ -114,9 +114,12 @@ def __deepcopy__(self, memo):
             instrumental_variables=copy.deepcopy(self.instrumental_variables),
             frontdoor_variables=copy.deepcopy(self.frontdoor_variables),
             mediator_variables=copy.deepcopy(self.mediator_variables),
+            mediation_first_stage_confounders=copy.deepcopy(self.mediation_first_stage_confounders),
+            mediation_second_stage_confounders=copy.deepcopy(self.mediation_second_stage_confounders),
             default_backdoor_id=copy.deepcopy(self.default_backdoor_id),
             default_adjustment_set_id=copy.deepcopy(self.default_adjustment_set_id),
             identifier_method=copy.deepcopy(self.identifier_method),
+            no_directed_path=self.no_directed_path,
         )
 
     def __str__(self, only_target_estimand: bool = False, show_all_backdoor_sets: bool = False):
diff --git a/tests/causal_identifiers/test_auto_identifier.py b/tests/causal_identifiers/test_auto_identifier.py
index 51c04daa6e..bf8b4b17fc 100644
--- a/tests/causal_identifiers/test_auto_identifier.py
+++ b/tests/causal_identifiers/test_auto_identifier.py
@@ -1,3 +1,5 @@
+import copy
+
 from dowhy.causal_identifier import AutoIdentifier
 from dowhy.causal_identifier.identify_effect import EstimandType
 from dowhy.graph import build_graph_from_str
@@ -15,3 +17,33 @@ def test_auto_identify_identifies_no_directed_path(self):
         assert identifier.identify_effect(
             graph, action_nodes=["B", "T"], outcome_nodes=["Y"], observed_nodes=["T", "Y", "A", "B"]
         ).no_directed_path
+
+    def test_deepcopy_preserves_all_fields(self):
+        """Regression test: __deepcopy__ must copy mediation confounders and no_directed_path."""
+        # Build NDE estimand with mediation confounders
+        graph = build_graph_from_str("digraph{T->M;T->Y;M->Y;W->T;W->Y;}")
+        identifier = AutoIdentifier(estimand_type=EstimandType.NONPARAMETRIC_NDE)
+        estimand = identifier.identify_effect(
+            graph,
+            action_nodes=["T"],
+            outcome_nodes=["Y"],
+            observed_nodes=["T", "M", "Y", "W"],
+        )
+        estimand_copy = copy.deepcopy(estimand)
+
+        assert estimand_copy.mediator_variables == estimand.mediator_variables
+        assert estimand_copy.mediation_first_stage_confounders == estimand.mediation_first_stage_confounders
+        assert estimand_copy.mediation_second_stage_confounders == estimand.mediation_second_stage_confounders
+        assert estimand_copy.no_directed_path == estimand.no_directed_path
+
+    def test_deepcopy_preserves_no_directed_path_flag(self):
+        """Regression test: deepcopy of an estimand with no directed path preserves the flag."""
+        graph = build_graph_from_str("digraph{T->Y;A->Y;A->B;}")
+        identifier = AutoIdentifier(estimand_type=EstimandType.NONPARAMETRIC_ATE)
+        estimand = identifier.identify_effect(
+            graph, action_nodes=["T", "B"], outcome_nodes=["Y"], observed_nodes=["T", "Y", "A", "B"]
+        )
+        assert estimand.no_directed_path
+
+        estimand_copy = copy.deepcopy(estimand)
+        assert estimand_copy.no_directed_path