Add skimage.viewer.qt wrapper.

This allows the viewer to use either PyQt4 or PySide as the toolkit.

skimage/viewer/__init__.py

@@ -1,4 +1 @@
-try:
-    from viewers import ImageViewer, CollectionViewer
-except ImportError:
-    print("Could not import PyQt4 -- ImageViewer not available.")
+from viewers import ImageViewer, CollectionViewer

skimage/viewer/plugins/base.py

@@ -1,18 +1,13 @@
 """
 Base class for Plugins that interact with ImageViewer.
 """
-try:
-    from PyQt4 import QtGui
-    from PyQt4.QtCore import Qt
-    from PyQt4.QtGui import QDialog
-except ImportError:
-    QDialog = object # hack to prevent nosetest and autodoc errors
-    print("Could not import PyQt4 -- skimage.viewer not available.")
+from ..qt import QtGui
+from ..qt.QtCore import Qt
 
 from ..utils import RequiredAttr, init_qtapp
 
 
-class Plugin(QDialog):
+class Plugin(QtGui.QDialog):
     """Base class for plugins that interact with an ImageViewer.
 
     A plugin connects an image filter (or another function) to an image viewer.

skimage/viewer/plugins/plotplugin.py

@@ -1,9 +1,5 @@
 import numpy as np
-
-try:
-    from PyQt4 import QtGui
-except ImportError:
-    print("Could not import PyQt4 -- skimage.viewer not available.")
+from ..qt import QtGui
 
 from ..utils import new_plot
 from .base import Plugin

skimage/viewer/qt/QtCore.py

@@ -0,0 +1,9 @@
+from . import qt_api
+
+if qt_api == 'pyside':
+    from PySide.QtCore import *
+elif qt_api == 'pyqt':
+    from PyQt4.QtCore import *
+else:
+    # Mock objects
+    Qt = None

skimage/viewer/qt/QtGui.py

@@ -0,0 +1,11 @@
+from . import qt_api
+
+if qt_api == 'pyside':
+    from PySide.QtGui import *
+elif qt_api == 'pyqt':
+    from PyQt4.QtGui import *
+else:
+    # Mock objects
+    QMainWindow = object
+    QDialog = object
+    QWidget = object

skimage/viewer/qt/README.rst

@@ -0,0 +1,5 @@
+This qt subpackage provides a wrapper to allow use of either PySide or PyQt4.
+In addition, if neither package is available, some mock objects are created to
+prevent errors in the TravisCI build. Only the objects used in the global
+namespace need to be mocked (e.g., a Qt object that gets subclassed is used
+in the global namespace).

skimage/viewer/qt/__init__.py

@@ -0,0 +1,19 @@
+import os
+import warnings
+
+qt_api = os.environ.get('QT_API')
+
+if qt_api is None:
+    try:
+        import PySide
+        qt_api = 'pyside'
+    except ImportError:
+        try:
+            import PyQt4
+            qt_api = 'pyqt'
+        except ImportError:
+            qt_api = 'none'
+            # Note that we don't want to raise an error because that would
+            # cause the TravisCI build to fail.
+            warnings.warn("Could not import PyQt4: ImageViewer not available!")
+    os.environ['QT_API'] = qt_api

skimage/viewer/utils/core.py

@@ -14,10 +14,7 @@ except ImportError:
     LinearSegmentedColormap = object
     print("Could not import matplotlib -- skimage.viewer not available.")
 
-try:
-    from PyQt4 import QtGui
-except ImportError:
-    print("Could not import PyQt4 -- skimage.viewer not available.")
+from ..qt import QtGui
 
 
 __all__ = ['init_qtapp', 'start_qtapp', 'RequiredAttr', 'figimage',

skimage/viewer/viewers/core.py

@@ -1,12 +1,8 @@
 """
 ImageViewer class for viewing and interacting with images.
 """
-try:
-    from PyQt4 import QtGui, QtCore
-    from PyQt4.QtGui import QMainWindow
-except ImportError:
-    QMainWindow = object  # hack to prevent nosetest and autodoc errors
-    print("Could not import PyQt4 -- skimage.viewer not available.")
+from ..qt import QtGui
+from ..qt import QtCore
 
 from skimage import io, img_as_float
 from skimage.util.dtype import dtype_range
@@ -32,7 +28,7 @@ def mpl_image_to_rgba(mpl_image):
     return img_as_float(image)
 
 
-class ImageViewer(QMainWindow):
+class ImageViewer(QtGui.QMainWindow):
     """Viewer for displaying images.
 
     This viewer is a simple container object that holds a Matplotlib axes

skimage/viewer/widgets/core.py

@@ -15,14 +15,9 @@ parameter type specified by its `ptype` attribute, which can be:
         property of the same name that updates the display.
 
 """
-try:
-    from PyQt4.QtCore import Qt
-    from PyQt4 import QtGui
-    from PyQt4 import QtCore
-    from PyQt4.QtGui import QWidget
-except ImportError:
-    QWidget = object  # hack to prevent nosetest and autodoc errors
-    print("Could not import PyQt4 -- skimage.viewer not available.")
+from ..qt import QtGui
+from ..qt import QtCore
+from ..qt.QtCore import Qt
 
 from ..utils import RequiredAttr
 
@@ -30,7 +25,7 @@ from ..utils import RequiredAttr
 __all__ = ['BaseWidget', 'Slider', 'ComboBox', 'Text']
 
 
-class BaseWidget(QWidget):
+class BaseWidget(QtGui.QWidget):
 
     plugin = RequiredAttr("Widget is not attached to a Plugin.")
 

skimage/viewer/widgets/history.py

@@ -1,9 +1,7 @@
 from textwrap import dedent
 
-try:
-    from PyQt4 import QtGui, QtCore
-except ImportError:
-    print("Could not import PyQt4 -- skimage.viewer not available.")
+from ..qt import QtGui
+from ..qt import QtCore
 
 import numpy as np