Make pygments optional for pyface.api (#796)

* Make it possible to import api even when pygments is not in the environment

pyface/api.py

@@ -28,8 +28,13 @@
 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:
+    from .python_editor import PythonEditor
+    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/tests/test_api.py

@@ -0,0 +1,166 @@
+# (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
+
+from traits.etsconfig.api import ETSConfig
+
+is_wx = (ETSConfig.toolkit == 'wx')
+is_qt = ETSConfig.toolkit.startswith('qt')
+
+
+class TestApi(unittest.TestCase):
+    """ Test importable items in any environment."""
+
+    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
+
+
+@unittest.skipIf(not is_qt, "This test is for qt.")
+class TestApiQt(unittest.TestCase):
+    """ Test importable items in a Qt environment."""
+
+    def test_importable_items_minimal(self):
+        # Test items should be importable in a minimal Qt environment
+        # Pygments is excused. Attempt to import PythonEditor or PythonShell
+        # will fail in an environment without pygments will fail, just as it
+        # would if these items were imported directly from the corresponding
+        # subpackages.
+        from pyface.api import (   # noqa: F401
+            AboutDialog,
+            Alignment,
+            Application,
+            ApplicationWindow,
+            Border,
+            CANCEL,
+            Clipboard,
+            ConfirmationDialog,
+            Dialog,
+            DirectoryDialog,
+            ExpandablePanel,
+            FileDialog,
+            Filter,
+            GUI,
+            GUIApplication,
+            HasBorder,
+            HasMargin,
+            HeadingText,
+            Image,
+            ImageCache,
+            ImageResource,
+            ImageWidget,
+            KeyPressedEvent,
+            LayeredPanel,
+            MDIApplicationWindow,
+            MDIWindowMenu,
+            Margin,
+            MessageDialog,
+            MultiToolbarWindow,
+            NO,
+            OK,
+            ProgressDialog,
+            # PythonEditor and PythonShell are omitted
+            SingleChoiceDialog,
+            Sorter,
+            SplashScreen,
+            SplitApplicationWindow,
+            SplitDialog,
+            SplitPanel,
+            SystemMetrics,
+            Widget,
+            Window,
+            YES,
+            beep,
+            choose_one,
+            clipboard,
+            confirm,
+            error,
+            information,
+            warning,
+        )
+
+    def test_python_editor_python_shell_importable(self):
+        # If pygments is in the environment, PythonEditor and PythonShell
+        # should be importable.
+        try:
+            import pygments        # noqa: F401
+        except ImportError:
+            raise self.skipTest("This test requires pygments.")
+
+        from pyface.api import (   # noqa: F401
+            PythonEditor,
+            PythonShell,
+        )
+
+
+@unittest.skipIf(not is_wx, "This test is for wx.")
+class TestApiWx(unittest.TestCase):
+    """ Test importable items in a wx environment."""
+
+    def test_importable_items(self):
+        # These items should always be importable for wx environment
+        from pyface.api import (   # noqa: F401
+            AboutDialog,
+            Alignment,
+            Application,
+            ApplicationWindow,
+            Border,
+            CANCEL,
+            Clipboard,
+            ConfirmationDialog,
+            Dialog,
+            DirectoryDialog,
+            ExpandablePanel,
+            FileDialog,
+            Filter,
+            GUI,
+            GUIApplication,
+            HasBorder,
+            HasMargin,
+            HeadingText,
+            Image,
+            ImageCache,
+            ImageResource,
+            ImageWidget,
+            KeyPressedEvent,
+            LayeredPanel,
+            MDIApplicationWindow,
+            MDIWindowMenu,
+            Margin,
+            MessageDialog,
+            MultiToolbarWindow,
+            NO,
+            OK,
+            ProgressDialog,
+            PythonEditor,
+            PythonShell,
+            SingleChoiceDialog,
+            Sorter,
+            SplashScreen,
+            SplitApplicationWindow,
+            SplitDialog,
+            SplitPanel,
+            SystemMetrics,
+            Widget,
+            Window,
+            YES,
+            beep,
+            choose_one,
+            clipboard,
+            confirm,
+            error,
+            fix_introspect_bug,
+            information,
+            warning,
+        )