From e4a635de87128de3b1d8b03e6d53bf9a15696cbc Mon Sep 17 00:00:00 2001
From: Pavol Juhas <juhas@google.com>
Date: Mon, 4 Nov 2024 11:41:45 -0800
Subject: [PATCH] pylint - fix dangerous-default-value

---
 dev_tools/.pylintrc                   | 2 +-
 unitary/quantum_chess/mcpe_utils.py   | 8 +++++---
 unitary/quantum_chess/swap_updater.py | 4 ++--
 3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/dev_tools/.pylintrc b/dev_tools/.pylintrc
index 515badfc..a5224ff9 100644
--- a/dev_tools/.pylintrc
+++ b/dev_tools/.pylintrc
@@ -16,7 +16,7 @@ enable=
     consider-merging-isinstance,
     consider-using-f-string,
     continue-in-finally,
-    # dangerous-default-value,  # TODO: #210 - enable and fix
+    dangerous-default-value,
     docstyle,
     duplicate-argument-name,
     # expression-not-assigned,  # TODO: #210 - enable and fix
diff --git a/unitary/quantum_chess/mcpe_utils.py b/unitary/quantum_chess/mcpe_utils.py
index 882cd412..7c12ef81 100644
--- a/unitary/quantum_chess/mcpe_utils.py
+++ b/unitary/quantum_chess/mcpe_utils.py
@@ -22,7 +22,7 @@
 """
 
 from collections import defaultdict, deque
-from typing import Callable, Dict, Iterable, Set, Tuple
+from typing import Callable, Dict, Iterable, Optional, Set, Tuple
 
 import cirq
 
@@ -67,8 +67,10 @@ class QubitMapping:
       initial_mapping: initial logical-to-physical qubit map.
     """
 
-    def __init__(self, initial_mapping: Dict[cirq.Qid, cirq.GridQubit] = {}):
-        self.logical_to_physical = initial_mapping
+    def __init__(
+        self, initial_mapping: Optional[Dict[cirq.Qid, cirq.GridQubit]] = None
+    ):
+        self.logical_to_physical = initial_mapping or {}
         self.physical_to_logical = {v: k for k, v in initial_mapping.items()}
 
     def swap_physical(self, q1: cirq.GridQubit, q2: cirq.GridQubit) -> None:
diff --git a/unitary/quantum_chess/swap_updater.py b/unitary/quantum_chess/swap_updater.py
index a836f0b8..4ad272fc 100644
--- a/unitary/quantum_chess/swap_updater.py
+++ b/unitary/quantum_chess/swap_updater.py
@@ -161,14 +161,14 @@ def __init__(
         self,
         circuit: cirq.Circuit,
         device_qubits: Optional[Iterable[cirq.GridQubit]],
-        initial_mapping: Dict[cirq.Qid, cirq.GridQubit] = {},
+        initial_mapping: Optional[Dict[cirq.Qid, cirq.GridQubit]] = None,
         swap_factory: Callable[
             [cirq.Qid, cirq.Qid], Iterable[cirq.Operation]
         ] = generate_decomposed_swap,
     ):
         self.device_qubits = device_qubits or []
         self.dlists = mcpe.DependencyLists(circuit)
-        self.mapping = mcpe.QubitMapping(initial_mapping)
+        self.mapping = mcpe.QubitMapping(initial_mapping or {})
         self.swap_factory = swap_factory
         self.adjacent = {q: q.neighbors(device_qubits) for q in self.device_qubits}
         self.pairwise_distances = _pairwise_shortest_distances(self.adjacent)