Log debug message if import PythonShell and PythonEditor fail in api.py

pyface/api.py

@@ -8,6 +8,7 @@
 #
 # Thanks for using Enthought open source!
 
+import logging as _logging
 
 from .about_dialog import AboutDialog
 from .application import Application
@@ -28,13 +29,22 @@
 from .key_pressed_event import KeyPressedEvent
 from .message_dialog import error, information, warning, MessageDialog
 from .progress_dialog import ProgressDialog
-try:
+
+from .util._optional_dependencies import optional_import as _optional_import
+
+# Excuse pygments dependency (for Qt), otherwise re-raise
+with _optional_import(
+        "pygments",
+        msg="PythonEditor not available due to missing pygments.",
+        logger=_logging.getLogger(__name__)):
     from .python_editor import PythonEditor
+
+with _optional_import(
+        "pygments",
+        msg="PythonShell not available due to missing pygments.",
+        logger=_logging.getLogger(__name__)):
     from .python_shell import PythonShell
-except ImportError as _exception:
-    # Excuse pygments dependency (for Qt), otherwise re-raise
-    if _exception.name != "pygments":
-        raise
+
 from .sorter import Sorter
 from .single_choice_dialog import choose_one, SingleChoiceDialog
 from .splash_screen import SplashScreen

pyface/util/_optional_dependencies.py

@@ -0,0 +1,38 @@
+
+# (C) Copyright 2005-2020 Enthought, Inc., Austin, TX
+# All rights reserved.
+#
+# This software is provided without warranty under the terms of the BSD
+# license included in LICENSE.txt and may be redistributed only under
+# the conditions described in the aforementioned license. The license
+# is also available online at http://www.enthought.com/licenses/BSD.txt
+#
+# Thanks for using Enthought open source!
+""" Utilities for handling optional import dependencies."""
+
+import contextlib
+
+
+@contextlib.contextmanager
+def optional_import(dependency_name, msg, logger):
+    """ Context manager for capturing ImportError for a particular optional
+    dependency. If such an error occurs, it will be silenced and a debug
+    message will be logged.
+
+    Parameters
+    ----------
+    dependency_name : str
+        Name of the module that may fail to be imported.
+        If matched, the ImportError will be silenced
+    msg : str
+        Log message to be emitted.
+    logger : Logger
+        Logger to use for logging messages.
+    """
+    try:
+        yield
+    except ImportError as exception:
+        if exception.name == dependency_name:
+            logger.debug(msg, exc_info=True)
+        else:
+            raise

pyface/util/tests/test__optional_dependencies.py

@@ -0,0 +1,38 @@
+# (C) Copyright 2005-2020 Enthought, Inc., Austin, TX
+# All rights reserved.
+#
+# This software is provided without warranty under the terms of the BSD
+# license included in LICENSE.txt and may be redistributed only under
+# the conditions described in the aforementioned license. The license
+# is also available online at http://www.enthought.com/licenses/BSD.txt
+#
+# Thanks for using Enthought open source!
+""" Tests for the _optional_dependencies module """
+
+import logging
+import unittest
+
+from pyface.util._optional_dependencies import optional_import
+
+
+class TestOptionalImport(unittest.TestCase):
+    """ Test optional import context manager """
+
+    def test_optional_import(self):
+        # Test excusing dependency and the logging behaviour
+        logger = logging.getLogger(self.id())
+        with self.assertLogs(logger, level="DEBUG") as log_context:
+            with optional_import(
+                    "random_missing_lib", "fail to import", logger):
+                # assume this library is not importable.
+                import random_missing_lib   # noqa: F401
+
+        log, = log_context.output
+        self.assertIn("fail to import", log)
+
+    def test_optional_import_reraise(self):
+        # Test if the import error was about something else, reraise
+        logger = logging.getLogger(self.id())
+        with self.assertRaises(ImportError):
+            with optional_import("some_random_lib", "", logger):
+                import some_random_missing_lib   # noqa: F401