Make pygments optional for pyface.api

pyface/api.py

@@ -28,8 +28,17 @@
 from .key_pressed_event import KeyPressedEvent
 from .message_dialog import error, information, warning, MessageDialog
 from .progress_dialog import ProgressDialog
-from .python_editor import PythonEditor
-from .python_shell import PythonShell
+
+try:
+    import pygments
+except ImportError:
+    # pygments is a runtime dependency for PythonEditor and PythonShell in Qt.
+    pass
+else:
+    del pygments
+    from .python_editor import PythonEditor
+    from .python_shell import PythonShell
+
 from .sorter import Sorter
 from .single_choice_dialog import choose_one, SingleChoiceDialog
 from .splash_screen import SplashScreen

pyface/tests/test_api.py

@@ -0,0 +1,21 @@
+# (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!
+
+""" Test for pyface.api """
+
+import unittest
+
+
+class TestApi(unittest.TestCase):
+
+    def test_api_importable(self):
+        # make sure api is importable with the most minimal
+        # required dependencies, including in the absence of toolkit backends.
+        from pyface import api   # noqa: F401