fix: Re-add ModuleNotFoundError handler for pandas_backports (#319)

* fix: bring back ModuleNotFoundError handler in pandas_backports.py

* add unit-test for import_default functions

Author: chelsea-lin

db_dtypes/pandas_backports.py

@@ -62,7 +62,10 @@ def import_default(module_name, force=False, default=None):
         return default
 
     name = default.__name__
-    module = __import__(module_name, {}, {}, [name])
+    try:
+        module = __import__(module_name, {}, {}, [name])
+    except ModuleNotFoundError:
+        return default
 
     return getattr(module, name, default)
 

tests/unit/test_pandas_backports.py

@@ -0,0 +1,37 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest.mock as mock
+
+import db_dtypes.pandas_backports as pandas_backports
+
+
+@mock.patch("builtins.__import__")
+def test_import_default_module_found(mock_import):
+    mock_module = mock.MagicMock()
+    mock_module.OpsMixin = "OpsMixin_from_module"  # Simulate successful import
+    mock_import.return_value = mock_module
+
+    default_class = type("OpsMixin", (), {})  # Dummy class
+    result = pandas_backports.import_default("module_name", default=default_class)
+    assert result == "OpsMixin_from_module"
+
+
+@mock.patch("builtins.__import__")
+def test_import_default_module_not_found(mock_import):
+    mock_import.side_effect = ModuleNotFoundError
+
+    default_class = type("OpsMixin", (), {})  # Dummy class
+    result = pandas_backports.import_default("module_name", default=default_class)
+    assert result == default_class