From 65c1d4eec674103a59d69e3fe21762df44c236de Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Sat, 27 Dec 2014 10:52:27 -0600
Subject: [PATCH 01/17] Update viewer for PyQt5 compatibility

Conflicts:
	skimage/viewer/tests/test_plugins.py
	skimage/viewer/tests/test_tools.py
---
 skimage/__init__.py                       |  8 ++++-
 skimage/viewer/__init__.py                | 14 +++------
 skimage/viewer/canvastools/base.py        |  5 +--
 skimage/viewer/canvastools/linetool.py    |  5 +--
 skimage/viewer/canvastools/painttool.py   | 11 +++----
 skimage/viewer/canvastools/recttool.py    |  6 +---
 skimage/viewer/plugins/base.py            | 16 +++-------
 skimage/viewer/plugins/color_histogram.py |  5 +--
 skimage/viewer/plugins/plotplugin.py      |  2 +-
 skimage/viewer/qt.py                      |  8 +++++
 skimage/viewer/qt/QtCore.py               | 22 -------------
 skimage/viewer/qt/QtGui.py                | 11 -------
 skimage/viewer/qt/README.rst              |  5 ---
 skimage/viewer/qt/__init__.py             | 22 -------------
 skimage/viewer/tests/test_plugins.py      | 33 +++++++++++++-------
 skimage/viewer/tests/test_tools.py        | 30 ++++++++++++++++++
 skimage/viewer/tests/test_utils.py        | 20 ++++++------
 skimage/viewer/tests/test_viewer.py       | 15 +++++----
 skimage/viewer/tests/test_widgets.py      | 27 +++++++++-------
 skimage/viewer/utils/core.py              | 31 ++++++------------
 skimage/viewer/utils/dialogs.py           |  2 +-
 skimage/viewer/viewers/core.py            | 32 ++++++++-----------
 skimage/viewer/widgets/core.py            | 38 ++++++++++-------------
 skimage/viewer/widgets/history.py         |  4 +--
 24 files changed, 161 insertions(+), 211 deletions(-)
 create mode 100644 skimage/viewer/qt.py
 delete mode 100644 skimage/viewer/qt/QtCore.py
 delete mode 100644 skimage/viewer/qt/QtGui.py
 delete mode 100644 skimage/viewer/qt/README.rst
 delete mode 100644 skimage/viewer/qt/__init__.py

diff --git a/skimage/__init__.py b/skimage/__init__.py
index fb38f87a..031ae075 100644
--- a/skimage/__init__.py
+++ b/skimage/__init__.py
@@ -60,7 +60,13 @@ import os.path as _osp
 import imp as _imp
 import functools as _functools
 import warnings as _warnings
-from skimage._shared.utils import deprecated as _deprecated
+
+import matplotlib as _mpl
+try:
+    _imp.find_module('PyQt5')
+    _mpl.use('Qt5Agg')
+except ImportError:
+    _mpl.use('Qt4Agg')
 
 pkg_dir = _osp.abspath(_osp.dirname(__file__))
 data_dir = _osp.join(pkg_dir, 'data')
diff --git a/skimage/viewer/__init__.py b/skimage/viewer/__init__.py
index 4bf70a93..365e00a2 100644
--- a/skimage/viewer/__init__.py
+++ b/skimage/viewer/__init__.py
@@ -1,11 +1,7 @@
-from warnings import warn
-from skimage._shared.version_requirements import is_installed
+try:
+    from .qt import QtGui as _QtGui
+except ImportError as e:
+    raise
+    raise ImportError('Viewer requires Qt')
 
 from .viewers import ImageViewer, CollectionViewer
-from .qt import qt_api
-
-viewer_available = not qt_api is None and is_installed('matplotlib')
-if not viewer_available:
-    warn('Viewer requires matplotlib and Qt')
-
-del qt_api, is_installed, warn
diff --git a/skimage/viewer/canvastools/base.py b/skimage/viewer/canvastools/base.py
index 197800c0..4b1d0c00 100644
--- a/skimage/viewer/canvastools/base.py
+++ b/skimage/viewer/canvastools/base.py
@@ -1,8 +1,5 @@
 import numpy as np
-try:
-    from matplotlib import lines
-except ImportError:
-    pass
+from matplotlib import lines
 
 __all__ = ['CanvasToolBase', 'ToolHandles']
 
diff --git a/skimage/viewer/canvastools/linetool.py b/skimage/viewer/canvastools/linetool.py
index f18a1915..58b05bc4 100644
--- a/skimage/viewer/canvastools/linetool.py
+++ b/skimage/viewer/canvastools/linetool.py
@@ -1,9 +1,6 @@
 import numpy as np
 
-try:
-    from matplotlib import lines
-except ImportError:
-    pass
+from matplotlib import lines
 from skimage.viewer.canvastools.base import CanvasToolBase, ToolHandles
 
 
diff --git a/skimage/viewer/canvastools/painttool.py b/skimage/viewer/canvastools/painttool.py
index 953f6ebe..9f4bb8ec 100644
--- a/skimage/viewer/canvastools/painttool.py
+++ b/skimage/viewer/canvastools/painttool.py
@@ -1,11 +1,8 @@
 import numpy as np
-try:
-    import matplotlib.pyplot as plt
-    import matplotlib.colors as mcolors
-    LABELS_CMAP = mcolors.ListedColormap(['white', 'red', 'dodgerblue', 'gold',
-                                          'greenyellow', 'blueviolet'])
-except ImportError:
-    pass
+import matplotlib.pyplot as plt
+import matplotlib.colors as mcolors
+LABELS_CMAP = mcolors.ListedColormap(['white', 'red', 'dodgerblue', 'gold',
+                                      'greenyellow', 'blueviolet'])
 from skimage.viewer.canvastools.base import CanvasToolBase
 
 
diff --git a/skimage/viewer/canvastools/recttool.py b/skimage/viewer/canvastools/recttool.py
index 4acccf8a..4520584e 100644
--- a/skimage/viewer/canvastools/recttool.py
+++ b/skimage/viewer/canvastools/recttool.py
@@ -1,8 +1,4 @@
-try:
-    from matplotlib.widgets import RectangleSelector
-except ImportError:
-    RectangleSelector = object
-
+from matplotlib.widgets import RectangleSelector
 from skimage.viewer.canvastools.base import CanvasToolBase
 from skimage.viewer.canvastools.base import ToolHandles
 
diff --git a/skimage/viewer/plugins/base.py b/skimage/viewer/plugins/base.py
index def0bfd9..7b0418b2 100644
--- a/skimage/viewer/plugins/base.py
+++ b/skimage/viewer/plugins/base.py
@@ -4,19 +4,11 @@ Base class for Plugins that interact with ImageViewer.
 from warnings import warn
 
 import numpy as np
-
-from ..qt import QtGui, qt_api
-from ..qt.QtCore import Qt, Signal
+from ..qt import QtWidgets, QtCore, Signal
 from ..utils import RequiredAttr, init_qtapp
-from skimage._shared.testing import doctest_skip_parser
-
-if qt_api is not None:
-    has_qt = True
-else:
-    has_qt = False
 
 
-class Plugin(QtGui.QDialog):
+class Plugin(QtWidgets.QDialog):
     """Base class for plugins that interact with an ImageViewer.
 
     A plugin connects an image filter (or another function) to an image viewer.
@@ -101,7 +93,7 @@ class Plugin(QtGui.QDialog):
                  "then the `image_filter` argument is ignored.")
 
         self.setWindowTitle(self.name)
-        self.layout = QtGui.QGridLayout(self)
+        self.layout = QtWidgets.QGridLayout(self)
         self.resize(width, height)
         self.row = 0
 
@@ -124,7 +116,7 @@ class Plugin(QtGui.QDialog):
         the image matches the filtered value specified by attached widgets.
         """
         self.setParent(image_viewer)
-        self.setWindowFlags(Qt.Dialog)
+        self.setWindowFlags(QtCore.Qt.Dialog)
 
         self.image_viewer = image_viewer
         self.image_viewer.plugins.append(self)
diff --git a/skimage/viewer/plugins/color_histogram.py b/skimage/viewer/plugins/color_histogram.py
index 52c71786..d6c6ddfc 100644
--- a/skimage/viewer/plugins/color_histogram.py
+++ b/skimage/viewer/plugins/color_histogram.py
@@ -1,8 +1,5 @@
 import numpy as np
-try:
-    import matplotlib.pyplot as plt
-except ImportError:
-    pass
+import matplotlib.pyplot as plt
 from skimage import color
 from skimage import exposure
 from .plotplugin import PlotPlugin
diff --git a/skimage/viewer/plugins/plotplugin.py b/skimage/viewer/plugins/plotplugin.py
index 5de6be7b..f995efa8 100644
--- a/skimage/viewer/plugins/plotplugin.py
+++ b/skimage/viewer/plugins/plotplugin.py
@@ -1,6 +1,6 @@
 import numpy as np
-from ..qt import QtGui
 
+from ..qt import QtGui
 from ..utils import new_plot
 from .base import Plugin
 
diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
new file mode 100644
index 00000000..bc827f9a
--- /dev/null
+++ b/skimage/viewer/qt.py
@@ -0,0 +1,8 @@
+try:
+    from matplotlib.backends.qt_compat import QtGui, QtCore, QtWidgets
+except ImportError:
+    from matplotlib.backends.qt4_compat import QtGui, QtCore
+    QtWidgets = QtGui
+
+Qt = QtCore.Qt
+Signal = QtCore.Signal
diff --git a/skimage/viewer/qt/QtCore.py b/skimage/viewer/qt/QtCore.py
deleted file mode 100644
index 19b92a53..00000000
--- a/skimage/viewer/qt/QtCore.py
+++ /dev/null
@@ -1,22 +0,0 @@
-from . import qt_api
-
-if qt_api == 'pyside':
-    from PySide.QtCore import *
-elif qt_api == 'pyqt':
-    from PyQt4.QtCore import *
-    # Use pyside names for signals and slots
-    Signal = pyqtSignal
-    Slot = pyqtSlot
-else:
-    # Mock objects for buildbot (which doesn't have Qt, but imports viewer).
-    class Qt(object):
-        TopDockWidgetArea = None
-        BottomDockWidgetArea = None
-        LeftDockWidgetArea = None
-        RightDockWidgetArea = None
-
-    def Signal(*args, **kwargs):
-        pass
-
-    def Slot(*args, **kwargs):
-        pass
diff --git a/skimage/viewer/qt/QtGui.py b/skimage/viewer/qt/QtGui.py
deleted file mode 100644
index 12e9837f..00000000
--- a/skimage/viewer/qt/QtGui.py
+++ /dev/null
@@ -1,11 +0,0 @@
-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
diff --git a/skimage/viewer/qt/README.rst b/skimage/viewer/qt/README.rst
deleted file mode 100644
index 993ae1a5..00000000
--- a/skimage/viewer/qt/README.rst
+++ /dev/null
@@ -1,5 +0,0 @@
-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).
diff --git a/skimage/viewer/qt/__init__.py b/skimage/viewer/qt/__init__.py
deleted file mode 100644
index 2fc4e946..00000000
--- a/skimage/viewer/qt/__init__.py
+++ /dev/null
@@ -1,22 +0,0 @@
-import os
-import warnings
-
-qt_api = os.environ.get('QT_API')
-
-if qt_api is None:
-    try:
-        import PyQt4
-        qt_api = 'pyqt'
-    except ImportError:
-        try:
-            import PySide
-            qt_api = 'pyside'
-        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!")
-
-
-if qt_api is not None:
-    os.environ['QT_API'] = qt_api
diff --git a/skimage/viewer/tests/test_plugins.py b/skimage/viewer/tests/test_plugins.py
index 528df8f4..b5cf7ab9 100644
--- a/skimage/viewer/tests/test_plugins.py
+++ b/skimage/viewer/tests/test_plugins.py
@@ -4,15 +4,26 @@ import skimage
 import skimage.data as data
 from skimage.filters.rank import median
 from skimage.morphology import disk
-from skimage.viewer import ImageViewer, viewer_available
+try:
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.plugins.base import Plugin
+    from skimage.viewer.widgets import Slider
+    from skimage.viewer.plugins import (
+        LineProfile, Measure, CannyPlugin, LabelPainter, Crop, ColorHistogram,
+        PlotPlugin)
+except ImportError:
+    ImageViewer is None
 from numpy.testing import assert_equal, assert_allclose, assert_almost_equal
 from numpy.testing.decorators import skipif
+<<<<<<< HEAD
 from skimage.viewer.plugins import (
     LineProfile, Measure, CannyPlugin, LabelPainter, Crop, ColorHistogram,
     PlotPlugin)
 from skimage.viewer.plugins.base import Plugin
 from skimage.viewer.widgets import Slider
 from skimage._shared._warnings import expected_warnings
+=======
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 
 
 def setup_line_profile(image, limits='image'):
@@ -22,7 +33,7 @@ def setup_line_profile(image, limits='image'):
     return plugin
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_line_profile():
     """ Test a line profile using an ndim=2 image"""
     plugin = setup_line_profile(data.camera())
@@ -36,7 +47,7 @@ def test_line_profile():
     assert_allclose(scan_data.mean(), 0.2812, rtol=1e-3)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_line_profile_rgb():
     """ Test a line profile using an ndim=3 image"""
     plugin = setup_line_profile(data.chelsea(), limits=None)
@@ -51,7 +62,7 @@ def test_line_profile_rgb():
     assert_allclose(scan_data.mean(), 0.4359, rtol=1e-3)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_line_profile_dynamic():
     """Test a line profile updating after an image transform"""
     image = data.coins()[:-50, :]  # shave some off to make the line lower
@@ -77,7 +88,7 @@ def test_line_profile_dynamic():
     assert_almost_equal(np.max(line) - np.min(line), 0.639, 1)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_measure():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -89,7 +100,7 @@ def test_measure():
     assert_equal(str(m._angle.text[:5]), '135.0')
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_canny():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -102,7 +113,7 @@ def test_canny():
     assert edges.sum() == 2852
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_label_painter():
     image = data.camera()
     moon = data.moon()
@@ -120,7 +131,7 @@ def test_label_painter():
     assert_equal(lp.paint_tool.shape, moon.shape)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_crop():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -131,7 +142,7 @@ def test_crop():
     assert_equal(viewer.image.shape, (101, 101))
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_color_histogram():
     image = skimage.img_as_float(data.load('color.png'))
     viewer = ImageViewer(image)
@@ -143,7 +154,7 @@ def test_color_histogram():
     assert_almost_equal(viewer.image.std(), 0.325, 3)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_plot_plugin():
     viewer = ImageViewer(data.moon())
     plugin = PlotPlugin(image_filter=lambda x: x)
@@ -155,7 +166,7 @@ def test_plot_plugin():
     viewer.close()
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_plugin():
     img = skimage.img_as_float(data.moon())
     viewer = ImageViewer(img)
diff --git a/skimage/viewer/tests/test_tools.py b/skimage/viewer/tests/test_tools.py
index 6b923063..6ea25940 100644
--- a/skimage/viewer/tests/test_tools.py
+++ b/skimage/viewer/tests/test_tools.py
@@ -4,12 +4,22 @@ import numpy as np
 from numpy.testing import assert_equal
 from numpy.testing.decorators import skipif
 from skimage import data
+<<<<<<< HEAD
 from skimage.viewer import ImageViewer, viewer_available
 from skimage.viewer.canvastools import (
     LineTool, ThickLineTool, RectangleTool, PaintTool)
 from skimage.viewer.canvastools.base import CanvasToolBase
 from matplotlib.testing.decorators import cleanup
 
+=======
+try:
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.canvastools import (
+        LineTool, ThickLineTool, RectangleTool, PaintTool)
+    from skimage.viewer.canvastools.base import CanvasToolBase
+except ImportError:
+    ImageViewer = None
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 
 
 def get_end_points(image):
@@ -74,8 +84,12 @@ def do_event(viewer, etype, button=1, xdata=0, ydata=0, key=None):
     func(event)
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_line_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -100,8 +114,12 @@ def test_line_tool():
     assert_equal(tool.geometry, np.array([[100, 100], [10, 10]]))
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_thick_line_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -124,8 +142,12 @@ def test_thick_line_tool():
     assert_equal(tool.linewidth, 1)
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_rect_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -153,8 +175,12 @@ def test_rect_tool():
     assert_equal(tool.geometry, [10, 100,  10, 100])
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_paint_tool():
     img = data.moon()
     viewer = ImageViewer(img)
@@ -187,8 +213,12 @@ def test_paint_tool():
     assert_equal(tool.overlay.sum(), 0)
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_base_tool():
     img = data.moon()
     viewer = ImageViewer(img)
diff --git a/skimage/viewer/tests/test_utils.py b/skimage/viewer/tests/test_utils.py
index 77f30299..5c962e5c 100644
--- a/skimage/viewer/tests/test_utils.py
+++ b/skimage/viewer/tests/test_utils.py
@@ -1,14 +1,14 @@
 # -*- coding: utf-8 -*-
-from skimage.viewer import viewer_available
-from skimage.viewer.qt import QtCore, QtGui
-from skimage.viewer import utils
-from skimage.viewer.utils import dialogs
+try:
+    from skimage.viewer import utils
+    from skimage.viewer.utils import dialogs
+    from skimage.viewer.qt import QtCore, QtGui
+except ImportError:
+    QtCore = None
 from numpy.testing.decorators import skipif
-from skimage.viewer import utils
-from skimage.viewer.utils import dialogs
 
 
-@skipif(not viewer_available)
+@skipif(QtCore is None)
 def test_event_loop():
     utils.init_qtapp()
     timer = QtCore.QTimer()
@@ -16,7 +16,7 @@ def test_event_loop():
     utils.start_qtapp()
 
 
-@skipif(not viewer_available)
+@skipif(QtCore is None)
 def test_format_filename():
     fname = dialogs._format_filename(('apple', 2))
     assert fname == 'apple'
@@ -24,7 +24,7 @@ def test_format_filename():
     assert fname is None
 
 
-@skipif(not viewer_available)
+@skipif(QtCore is None)
 def test_open_file_dialog():
     utils.init_qtapp()
     timer = QtCore.QTimer()
@@ -33,7 +33,7 @@ def test_open_file_dialog():
     assert filename is None
 
 
-@skipif(not viewer_available)
+@skipif(QtCore is None)
 def test_save_file_dialog():
     utils.init_qtapp()
     timer = QtCore.QTimer()
diff --git a/skimage/viewer/tests/test_viewer.py b/skimage/viewer/tests/test_viewer.py
index 1604ca6d..0709d18d 100644
--- a/skimage/viewer/tests/test_viewer.py
+++ b/skimage/viewer/tests/test_viewer.py
@@ -1,9 +1,12 @@
 
 from skimage import data
-from skimage.viewer.qt import QtGui, QtCore
-from skimage.viewer import ImageViewer, CollectionViewer, viewer_available
+try:
+    from skimage.viewer.qt import QtGui, QtCore
+    from skimage.viewer import ImageViewer, CollectionViewer
+    from skimage.viewer.plugins import OverlayPlugin
+except ImportError:
+    ImageViewer = None
 from skimage.transform import pyramid_gaussian
-from skimage.viewer.plugins import OverlayPlugin
 from skimage.filters import sobel
 from numpy.testing import assert_equal
 from numpy.testing.decorators import skipif
@@ -11,7 +14,7 @@ from skimage._shared.version_requirements import is_installed
 from skimage._shared._warnings import expected_warnings
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_viewer():
     astro = data.astronaut()
     coins = data.coins()
@@ -38,7 +41,7 @@ def make_key_event(key):
                            QtCore.Qt.NoModifier)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_collection_viewer():
 
     img = data.astronaut()
@@ -54,7 +57,7 @@ def test_collection_viewer():
     view._format_coord(10, 10)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 @skipif(not is_installed('matplotlib', '>=1.2'))
 def test_viewer_with_overlay():
     img = data.coins()
diff --git a/skimage/viewer/tests/test_widgets.py b/skimage/viewer/tests/test_widgets.py
index 170c186c..8e76d29b 100644
--- a/skimage/viewer/tests/test_widgets.py
+++ b/skimage/viewer/tests/test_widgets.py
@@ -1,11 +1,14 @@
 
 import os
 from skimage import data, img_as_float, io, img_as_uint
-from skimage.viewer import ImageViewer, viewer_available
-from skimage.viewer.widgets import (
-    Slider, OKCancelButtons, SaveButtons, ComboBox, CheckBox, Text)
-from skimage.viewer.plugins.base import Plugin
-from skimage.viewer.qt import QtGui, QtCore
+try:
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.qt import QtGui, QtCore
+    from skimage.viewer.widgets import (
+        Slider, OKCancelButtons, SaveButtons, ComboBox, CheckBox, Text)
+    from skimage.viewer.plugins.base import Plugin
+except ImportError:
+    ImageViewer = None
 from numpy.testing import assert_almost_equal, assert_equal
 from numpy.testing.decorators import skipif
 from skimage._shared._warnings import expected_warnings
@@ -18,7 +21,7 @@ def get_image_viewer():
     return viewer
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_check_box():
     viewer = get_image_viewer()
     cb = CheckBox('hello', value=True, alignment='left')
@@ -33,7 +36,7 @@ def test_check_box():
     assert_equal(cb.val, False)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_combo_box():
     viewer = get_image_viewer()
     cb = ComboBox('hello', ('a', 'b', 'c'))
@@ -46,7 +49,7 @@ def test_combo_box():
     assert_equal(cb.index, 2)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_text_widget():
     viewer = get_image_viewer()
     txt = Text('hello', 'hello, world!')
@@ -57,7 +60,7 @@ def test_text_widget():
     assert_equal(str(txt.text), 'goodbye, world!')
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_slider_int():
     viewer = get_image_viewer()
     sld = Slider('radius', 2, 10, value_type='int')
@@ -71,7 +74,7 @@ def test_slider_int():
     assert_equal(sld.val, 5)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_slider_float():
     viewer = get_image_viewer()
     sld = Slider('alpha', 2.1, 3.1, value=2.1, value_type='float',
@@ -86,7 +89,7 @@ def test_slider_float():
     assert_almost_equal(sld.val, 2.5, 2)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_save_buttons():
     viewer = get_image_viewer()
     sv = SaveButtons()
@@ -114,7 +117,7 @@ def test_save_buttons():
     os.remove(filename)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_ok_buttons():
     viewer = get_image_viewer()
     ok = OKCancelButtons()
diff --git a/skimage/viewer/utils/core.py b/skimage/viewer/utils/core.py
index 242f2de4..dd81d2a7 100644
--- a/skimage/viewer/utils/core.py
+++ b/skimage/viewer/utils/core.py
@@ -1,28 +1,17 @@
 import warnings
 
 import numpy as np
+from skimage.viewer.qt import QtGui
+import matplotlib as mpl
+from matplotlib.figure import Figure
+from matplotlib import _pylab_helpers
+from matplotlib.colors import LinearSegmentedColormap
 
-from ..qt import qt_api
-
-try:
-    import matplotlib as mpl
-    from matplotlib.figure import Figure
-    from matplotlib import _pylab_helpers
-    from matplotlib.colors import LinearSegmentedColormap
-    if not qt_api is None:
-        from matplotlib.backends.backend_qt4 import FigureManagerQT
-        from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
-        if 'agg' not in mpl.get_backend().lower():
-            print("Recommended matplotlib backend is `Agg` for full "
-                  "skimage.viewer functionality.")
-    else:
-        FigureCanvasQTAgg = object
-        LinearSegmentedColormap = object
-except ImportError:
-    FigureCanvasQTAgg = object  # hack to prevent nosetest and autodoc errors
-    LinearSegmentedColormap = object
-
-from ..qt import QtGui
+from matplotlib.backends.backend_qt4 import FigureManagerQT
+from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
+if 'agg' not in mpl.get_backend().lower():
+    warnings.warn("Recommended matplotlib backend is `Agg` for full "
+          "skimage.viewer functionality.")
 
 
 __all__ = ['init_qtapp', 'start_qtapp', 'RequiredAttr', 'figimage',
diff --git a/skimage/viewer/utils/dialogs.py b/skimage/viewer/utils/dialogs.py
index f160531d..20dd0e16 100644
--- a/skimage/viewer/utils/dialogs.py
+++ b/skimage/viewer/utils/dialogs.py
@@ -1,6 +1,6 @@
 import os
 
-from ..qt import QtGui
+from skimage.viewer.qt import QtGui
 
 
 __all__ = ['open_file_dialog', 'save_file_dialog']
diff --git a/skimage/viewer/viewers/core.py b/skimage/viewer/viewers/core.py
index 36ba6ee6..19112dc1 100644
--- a/skimage/viewer/viewers/core.py
+++ b/skimage/viewer/viewers/core.py
@@ -1,21 +1,15 @@
 """
 ImageViewer class for viewing and interacting with images.
 """
-from ..qt import QtGui, qt_api
-from ..qt.QtCore import Qt, Signal
-
-if qt_api is not None:
-    has_qt = True
-else:
-    has_qt = False
 
+from skimage.viewer.qt import QtWidgets, Qt, Signal
 from skimage import io, img_as_float
 from skimage.util.dtype import dtype_range
 from skimage.exposure import rescale_intensity
 import numpy as np
-from .. import utils
 from ..widgets import Slider
-from ..utils import dialogs
+from ..utils import (
+    dialogs, init_qtapp, figimage, start_qtapp, update_axes_image)
 from ..plugins.base import Plugin
 
 
@@ -152,7 +146,7 @@ class EventManager(object):
             tool.on_scroll(event)
 
 
-class ImageViewer(QtGui.QMainWindow):
+class ImageViewer(QtWidgets.QMainWindow):
     """Viewer for displaying images.
 
     This viewer is a simple container object that holds a Matplotlib axes
@@ -194,7 +188,7 @@ class ImageViewer(QtGui.QMainWindow):
 
     def __init__(self, image, useblit=True):
         # Start main loop
-        utils.init_qtapp()
+        init_qtapp()
         super(ImageViewer, self).__init__()
 
         #TODO: Add ImageViewer to skimage.io window manager
@@ -202,7 +196,7 @@ class ImageViewer(QtGui.QMainWindow):
         self.setAttribute(Qt.WA_DeleteOnClose)
         self.setWindowTitle("Image Viewer")
 
-        self.file_menu = QtGui.QMenu('&File', self)
+        self.file_menu = QtWidgets.QMenu('&File', self)
         self.file_menu.addAction('Open file', self.open_file,
                                  Qt.CTRL + Qt.Key_O)
         self.file_menu.addAction('Save to file', self.save_to_file,
@@ -211,7 +205,7 @@ class ImageViewer(QtGui.QMainWindow):
                                  Qt.CTRL + Qt.Key_Q)
         self.menuBar().addMenu(self.file_menu)
 
-        self.main_widget = QtGui.QWidget()
+        self.main_widget = QtWidgets.QWidget()
         self.setCentralWidget(self.main_widget)
 
         if isinstance(image, Plugin):
@@ -221,7 +215,7 @@ class ImageViewer(QtGui.QMainWindow):
             # When plugin is started, start
             plugin._started.connect(self._show)
 
-        self.fig, self.ax = utils.figimage(image)
+        self.fig, self.ax = figimage(image)
         self.canvas = self.fig.canvas
         self.canvas.setParent(self)
         self.ax.autoscale(enable=False)
@@ -236,7 +230,7 @@ class ImageViewer(QtGui.QMainWindow):
         self._update_original_image(image)
         self.plugins = []
 
-        self.layout = QtGui.QVBoxLayout(self.main_widget)
+        self.layout = QtWidgets.QVBoxLayout(self.main_widget)
         self.layout.addWidget(self.canvas)
 
         status_bar = self.statusBar()
@@ -255,7 +249,7 @@ class ImageViewer(QtGui.QMainWindow):
         if plugin.dock:
             location = self.dock_areas[plugin.dock]
             dock_location = Qt.DockWidgetArea(location)
-            dock = QtGui.QDockWidget()
+            dock = QtWidgets.QDockWidget()
             dock.setWidget(plugin)
             dock.setWindowTitle(plugin.name)
             self.addDockWidget(dock_location, dock)
@@ -341,7 +335,7 @@ class ImageViewer(QtGui.QMainWindow):
         """
         self._show()
         if main_window:
-            utils.start_qtapp()
+            start_qtapp()
         return [p.output() for p in self.plugins]
 
     def redraw(self):
@@ -357,7 +351,7 @@ class ImageViewer(QtGui.QMainWindow):
     @image.setter
     def image(self, image):
         self._img = image
-        utils.update_axes_image(self._image_plot, image)
+        update_axes_image(self._image_plot, image)
 
         # update display (otherwise image doesn't fill the canvas)
         h, w = image.shape[:2]
@@ -487,7 +481,7 @@ class CollectionViewer(ImageViewer):
         self._update_original_image(image)
 
     def keyPressEvent(self, event):
-        if type(event) == QtGui.QKeyEvent:
+        if type(event) == QtWidgets.QKeyEvent:
             key = event.key()
             # Number keys (code: 0 = key 48, 9 = key 57) move to deciles
             if 48 <= key < 58:
diff --git a/skimage/viewer/widgets/core.py b/skimage/viewer/widgets/core.py
index 4da8925b..ae8be4e7 100644
--- a/skimage/viewer/widgets/core.py
+++ b/skimage/viewer/widgets/core.py
@@ -15,17 +15,15 @@ parameter type specified by its `ptype` attribute, which can be:
         property of the same name that updates the display.
 
 """
-from ..qt import QtGui
-from ..qt import QtCore
-from ..qt.QtCore import Qt
-
+from ..qt import QtWidgets, QtCore, Qt
 from ..utils import RequiredAttr
 
 
 __all__ = ['BaseWidget', 'Slider', 'ComboBox', 'CheckBox', 'Text']
 
 
-class BaseWidget(QtGui.QWidget):
+
+class BaseWidget(QtWidgets.QWidget):
 
     plugin = RequiredAttr("Widget is not attached to a Plugin.")
 
@@ -49,11 +47,11 @@ class Text(BaseWidget):
 
     def __init__(self, name=None, text=''):
         super(Text, self).__init__(name)
-        self._label = QtGui.QLabel()
+        self._label = QtWidgets.QLabel()
         self.text = text
-        self.layout = QtGui.QHBoxLayout(self)
+        self.layout = QtWidgets.QHBoxLayout(self)
         if name is not None:
-            name_label = QtGui.QLabel()
+            name_label = QtWidgets.QLabel()
             name_label.setText(name)
             self.layout.addWidget(name_label)
         self.layout.addWidget(self._label)
@@ -105,17 +103,17 @@ class Slider(BaseWidget):
         # Set widget orientation
         #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         if orientation == 'vertical':
-            self.slider = QtGui.QSlider(Qt.Vertical)
+            self.slider = QtWidgets.QSlider(Qt.Vertical)
             alignment = QtCore.Qt.AlignHCenter
             align_text = QtCore.Qt.AlignHCenter
             align_value = QtCore.Qt.AlignHCenter
-            self.layout = QtGui.QVBoxLayout(self)
+            self.layout = QtWidgets.QVBoxLayout(self)
         elif orientation == 'horizontal':
-            self.slider = QtGui.QSlider(Qt.Horizontal)
+            self.slider = QtWidgets.QSlider(Qt.Horizontal)
             alignment = QtCore.Qt.AlignVCenter
             align_text = QtCore.Qt.AlignLeft
             align_value = QtCore.Qt.AlignRight
-            self.layout = QtGui.QHBoxLayout(self)
+            self.layout = QtWidgets.QHBoxLayout(self)
         else:
             msg = "Unexpected value %s for 'orientation'"
             raise ValueError(msg % orientation)
@@ -151,11 +149,11 @@ class Slider(BaseWidget):
             raise ValueError("Unexpected value %s for 'update_on'" % update_on)
         self.slider.setFocusPolicy(QtCore.Qt.StrongFocus)
 
-        self.name_label = QtGui.QLabel()
+        self.name_label = QtWidgets.QLabel()
         self.name_label.setText(self.name)
         self.name_label.setAlignment(align_text)
 
-        self.editbox = QtGui.QLineEdit()
+        self.editbox = QtWidgets.QLineEdit()
         self.editbox.setMaximumWidth(max_edit_width)
         self.editbox.setText(self.value_fmt % self.val)
         self.editbox.setAlignment(align_value)
@@ -229,20 +227,18 @@ class ComboBox(BaseWidget):
     def __init__(self, name, items, ptype='kwarg', callback=None):
         super(ComboBox, self).__init__(name, ptype, callback)
 
-        self.name_label = QtGui.QLabel()
+        self.name_label = QtWidgets.QLabel()
         self.name_label.setText(self.name)
         self.name_label.setAlignment(QtCore.Qt.AlignLeft)
 
-        self._combo_box = QtGui.QComboBox()
+        self._combo_box = QtWidgets.QComboBox()
         self._combo_box.addItems(list(items))
 
-        self.layout = QtGui.QHBoxLayout(self)
+        self.layout = QtWidgets.QHBoxLayout(self)
         self.layout.addWidget(self.name_label)
         self.layout.addWidget(self._combo_box)
 
         self._combo_box.currentIndexChanged.connect(self._value_changed)
-        # self.connect(self._combo_box,
-                # SIGNAL("currentIndexChanged(int)"), self.updateUi)
 
     @property
     def val(self):
@@ -283,11 +279,11 @@ class CheckBox(BaseWidget):
                  callback=None):
         super(CheckBox, self).__init__(name, ptype, callback)
 
-        self._check_box = QtGui.QCheckBox()
+        self._check_box = QtWidgets.QCheckBox()
         self._check_box.setChecked(value)
         self._check_box.setText(self.name)
 
-        self.layout = QtGui.QHBoxLayout(self)
+        self.layout = QtWidgets.QHBoxLayout(self)
         if alignment == 'center':
             self.layout.setAlignment(QtCore.Qt.AlignCenter)
         elif alignment == 'left':
diff --git a/skimage/viewer/widgets/history.py b/skimage/viewer/widgets/history.py
index d1df8689..ba0f0cd3 100644
--- a/skimage/viewer/widgets/history.py
+++ b/skimage/viewer/widgets/history.py
@@ -1,8 +1,6 @@
 from textwrap import dedent
 
-from ..qt import QtGui
-from ..qt import QtCore
-
+from ..qt import QtGui, QtCore
 import numpy as np
 
 import skimage

From 47065d733c6cebafb4ca37decb9280e4e7b31b6f Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Tue, 23 Dec 2014 21:42:43 -0600
Subject: [PATCH 02/17] Use a smarter backend selection

---
 skimage/__init__.py | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/skimage/__init__.py b/skimage/__init__.py
index 031ae075..f7339ba5 100644
--- a/skimage/__init__.py
+++ b/skimage/__init__.py
@@ -62,11 +62,10 @@ import functools as _functools
 import warnings as _warnings
 
 import matplotlib as _mpl
-try:
-    _imp.find_module('PyQt5')
-    _mpl.use('Qt5Agg')
-except ImportError:
-    _mpl.use('Qt4Agg')
+if 'Qt5Agg' in _mpl.rcsetup.interactive_bk:
+    _mpl.rcParams['backend'] = 'Qt5Agg'
+else:
+    _mpl.rcParams['backend'] = 'Qt4Agg'
 
 pkg_dir = _osp.abspath(_osp.dirname(__file__))
 data_dir = _osp.join(pkg_dir, 'data')

From 297ccea8b0a0fde4e89509f723502ba6c8b861d2 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Tue, 23 Dec 2014 22:02:21 -0600
Subject: [PATCH 03/17] Do not try and guess the mpl backend

---
 skimage/__init__.py | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/skimage/__init__.py b/skimage/__init__.py
index f7339ba5..303ea34f 100644
--- a/skimage/__init__.py
+++ b/skimage/__init__.py
@@ -61,12 +61,6 @@ import imp as _imp
 import functools as _functools
 import warnings as _warnings
 
-import matplotlib as _mpl
-if 'Qt5Agg' in _mpl.rcsetup.interactive_bk:
-    _mpl.rcParams['backend'] = 'Qt5Agg'
-else:
-    _mpl.rcParams['backend'] = 'Qt4Agg'
-
 pkg_dir = _osp.abspath(_osp.dirname(__file__))
 data_dir = _osp.join(pkg_dir, 'data')
 

From 68508576f6a462653f1ad367a29aede384e31152 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 06:06:01 -0600
Subject: [PATCH 04/17] Remove debug raise

---
 skimage/viewer/__init__.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/skimage/viewer/__init__.py b/skimage/viewer/__init__.py
index 365e00a2..2ae55ed4 100644
--- a/skimage/viewer/__init__.py
+++ b/skimage/viewer/__init__.py
@@ -1,7 +1,6 @@
 try:
     from .qt import QtGui as _QtGui
 except ImportError as e:
-    raise
     raise ImportError('Viewer requires Qt')
 
 from .viewers import ImageViewer, CollectionViewer

From 8d40cbd1d2cf431454dcfd9a9088be73687e7c1a Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 06:38:20 -0600
Subject: [PATCH 05/17] Allow viewer package to import without Qt

---
 skimage/viewer/__init__.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/skimage/viewer/__init__.py b/skimage/viewer/__init__.py
index 2ae55ed4..8c2c33cf 100644
--- a/skimage/viewer/__init__.py
+++ b/skimage/viewer/__init__.py
@@ -1,6 +1,5 @@
+import warnings
 try:
-    from .qt import QtGui as _QtGui
+    from .viewers import ImageViewer, CollectionViewer
 except ImportError as e:
-    raise ImportError('Viewer requires Qt')
-
-from .viewers import ImageViewer, CollectionViewer
+    warnings.warn('Viewer requires Qt')

From 6f57873526741458a343b7d9a131f568d3e79e0a Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Sat, 27 Dec 2014 10:54:13 -0600
Subject: [PATCH 06/17] Do not use ImportError behaviour in viewer

Conflicts:
	skimage/viewer/tests/test_tools.py
---
 skimage/viewer/__init__.py           |  7 +++--
 skimage/viewer/qt.py                 | 21 ++++++++++++--
 skimage/viewer/tests/test_plugins.py | 35 +++++++++++-----------
 skimage/viewer/tests/test_tools.py   | 43 ++++------------------------
 skimage/viewer/tests/test_utils.py   | 17 +++++------
 skimage/viewer/tests/test_viewer.py  | 17 ++++++-----
 skimage/viewer/tests/test_widgets.py | 29 +++++++++----------
 7 files changed, 74 insertions(+), 95 deletions(-)

diff --git a/skimage/viewer/__init__.py b/skimage/viewer/__init__.py
index 8c2c33cf..443e5659 100644
--- a/skimage/viewer/__init__.py
+++ b/skimage/viewer/__init__.py
@@ -1,5 +1,6 @@
 import warnings
-try:
-    from .viewers import ImageViewer, CollectionViewer
-except ImportError as e:
+from .viewers import ImageViewer, CollectionViewer
+from .qt import has_qt
+
+if not has_qt:
     warnings.warn('Viewer requires Qt')
diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index bc827f9a..dc4852c9 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -1,8 +1,25 @@
+has_qt = True
+
 try:
     from matplotlib.backends.qt_compat import QtGui, QtCore, QtWidgets
 except ImportError:
-    from matplotlib.backends.qt4_compat import QtGui, QtCore
-    QtWidgets = QtGui
+    try:
+        from matplotlib.backends.qt4_compat import QtGui, QtCore
+        QtWidgets = QtGui
+    except ImportError:
+        # Mock objects
+        class QtGui(object):
+            QMainWindow = object
+            QDialog = object
+            QWidget = object
+
+        class QtCore(object):
+            Signal = object
+            Qt = object
+
+        QtWidgets = QtGui
+
+        has_qt = False
 
 Qt = QtCore.Qt
 Signal = QtCore.Signal
diff --git a/skimage/viewer/tests/test_plugins.py b/skimage/viewer/tests/test_plugins.py
index b5cf7ab9..699578f2 100644
--- a/skimage/viewer/tests/test_plugins.py
+++ b/skimage/viewer/tests/test_plugins.py
@@ -4,15 +4,12 @@ import skimage
 import skimage.data as data
 from skimage.filters.rank import median
 from skimage.morphology import disk
-try:
-    from skimage.viewer import ImageViewer
-    from skimage.viewer.plugins.base import Plugin
-    from skimage.viewer.widgets import Slider
-    from skimage.viewer.plugins import (
-        LineProfile, Measure, CannyPlugin, LabelPainter, Crop, ColorHistogram,
-        PlotPlugin)
-except ImportError:
-    ImageViewer is None
+from skimage.viewer import ImageViewer, has_qt
+from skimage.viewer.plugins.base import Plugin
+from skimage.viewer.widgets import Slider
+from skimage.viewer.plugins import (
+    LineProfile, Measure, CannyPlugin, LabelPainter, Crop, ColorHistogram,
+    PlotPlugin)
 from numpy.testing import assert_equal, assert_allclose, assert_almost_equal
 from numpy.testing.decorators import skipif
 <<<<<<< HEAD
@@ -33,7 +30,7 @@ def setup_line_profile(image, limits='image'):
     return plugin
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_line_profile():
     """ Test a line profile using an ndim=2 image"""
     plugin = setup_line_profile(data.camera())
@@ -47,7 +44,7 @@ def test_line_profile():
     assert_allclose(scan_data.mean(), 0.2812, rtol=1e-3)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_line_profile_rgb():
     """ Test a line profile using an ndim=3 image"""
     plugin = setup_line_profile(data.chelsea(), limits=None)
@@ -62,7 +59,7 @@ def test_line_profile_rgb():
     assert_allclose(scan_data.mean(), 0.4359, rtol=1e-3)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_line_profile_dynamic():
     """Test a line profile updating after an image transform"""
     image = data.coins()[:-50, :]  # shave some off to make the line lower
@@ -88,7 +85,7 @@ def test_line_profile_dynamic():
     assert_almost_equal(np.max(line) - np.min(line), 0.639, 1)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_measure():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -100,7 +97,7 @@ def test_measure():
     assert_equal(str(m._angle.text[:5]), '135.0')
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_canny():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -113,7 +110,7 @@ def test_canny():
     assert edges.sum() == 2852
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_label_painter():
     image = data.camera()
     moon = data.moon()
@@ -131,7 +128,7 @@ def test_label_painter():
     assert_equal(lp.paint_tool.shape, moon.shape)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_crop():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -142,7 +139,7 @@ def test_crop():
     assert_equal(viewer.image.shape, (101, 101))
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_color_histogram():
     image = skimage.img_as_float(data.load('color.png'))
     viewer = ImageViewer(image)
@@ -154,7 +151,7 @@ def test_color_histogram():
     assert_almost_equal(viewer.image.std(), 0.325, 3)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_plot_plugin():
     viewer = ImageViewer(data.moon())
     plugin = PlotPlugin(image_filter=lambda x: x)
@@ -166,7 +163,7 @@ def test_plot_plugin():
     viewer.close()
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_plugin():
     img = skimage.img_as_float(data.moon())
     viewer = ImageViewer(img)
diff --git a/skimage/viewer/tests/test_tools.py b/skimage/viewer/tests/test_tools.py
index 6ea25940..aae44783 100644
--- a/skimage/viewer/tests/test_tools.py
+++ b/skimage/viewer/tests/test_tools.py
@@ -4,23 +4,12 @@ import numpy as np
 from numpy.testing import assert_equal
 from numpy.testing.decorators import skipif
 from skimage import data
-<<<<<<< HEAD
-from skimage.viewer import ImageViewer, viewer_available
+from skimage.viewer import ImageViewer, has_qt
 from skimage.viewer.canvastools import (
     LineTool, ThickLineTool, RectangleTool, PaintTool)
 from skimage.viewer.canvastools.base import CanvasToolBase
 from matplotlib.testing.decorators import cleanup
 
-=======
-try:
-    from skimage.viewer import ImageViewer
-    from skimage.viewer.canvastools import (
-        LineTool, ThickLineTool, RectangleTool, PaintTool)
-    from skimage.viewer.canvastools.base import CanvasToolBase
-except ImportError:
-    ImageViewer = None
->>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
-
 
 def get_end_points(image):
     h, w = image.shape[0:2]
@@ -84,12 +73,8 @@ def do_event(viewer, etype, button=1, xdata=0, ydata=0, key=None):
     func(event)
 
 
-<<<<<<< HEAD
 @cleanup
-@skipif(not viewer_available)
-=======
-@skipif(ImageViewer is None)
->>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
+@skipif(not has_qt)
 def test_line_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -114,12 +99,8 @@ def test_line_tool():
     assert_equal(tool.geometry, np.array([[100, 100], [10, 10]]))
 
 
-<<<<<<< HEAD
 @cleanup
-@skipif(not viewer_available)
-=======
-@skipif(ImageViewer is None)
->>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
+@skipif(not has_qt)
 def test_thick_line_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -142,12 +123,8 @@ def test_thick_line_tool():
     assert_equal(tool.linewidth, 1)
 
 
-<<<<<<< HEAD
 @cleanup
-@skipif(not viewer_available)
-=======
-@skipif(ImageViewer is None)
->>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
+@skipif(not has_qt)
 def test_rect_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -175,12 +152,8 @@ def test_rect_tool():
     assert_equal(tool.geometry, [10, 100,  10, 100])
 
 
-<<<<<<< HEAD
 @cleanup
-@skipif(not viewer_available)
-=======
-@skipif(ImageViewer is None)
->>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
+@skipif(not has_qt)
 def test_paint_tool():
     img = data.moon()
     viewer = ImageViewer(img)
@@ -213,12 +186,8 @@ def test_paint_tool():
     assert_equal(tool.overlay.sum(), 0)
 
 
-<<<<<<< HEAD
 @cleanup
-@skipif(not viewer_available)
-=======
-@skipif(ImageViewer is None)
->>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
+@skipif(not has_qt)
 def test_base_tool():
     img = data.moon()
     viewer = ImageViewer(img)
diff --git a/skimage/viewer/tests/test_utils.py b/skimage/viewer/tests/test_utils.py
index 5c962e5c..ae158a90 100644
--- a/skimage/viewer/tests/test_utils.py
+++ b/skimage/viewer/tests/test_utils.py
@@ -1,14 +1,11 @@
 # -*- coding: utf-8 -*-
-try:
-    from skimage.viewer import utils
-    from skimage.viewer.utils import dialogs
-    from skimage.viewer.qt import QtCore, QtGui
-except ImportError:
-    QtCore = None
+from skimage.viewer import utils
+from skimage.viewer.utils import dialogs
+from skimage.viewer.qt import QtCore, QtGui, has_qt
 from numpy.testing.decorators import skipif
 
 
-@skipif(QtCore is None)
+@skipif(not has_qt)
 def test_event_loop():
     utils.init_qtapp()
     timer = QtCore.QTimer()
@@ -16,7 +13,7 @@ def test_event_loop():
     utils.start_qtapp()
 
 
-@skipif(QtCore is None)
+@skipif(not has_qt)
 def test_format_filename():
     fname = dialogs._format_filename(('apple', 2))
     assert fname == 'apple'
@@ -24,7 +21,7 @@ def test_format_filename():
     assert fname is None
 
 
-@skipif(QtCore is None)
+@skipif(not has_qt)
 def test_open_file_dialog():
     utils.init_qtapp()
     timer = QtCore.QTimer()
@@ -33,7 +30,7 @@ def test_open_file_dialog():
     assert filename is None
 
 
-@skipif(QtCore is None)
+@skipif(not has_qt)
 def test_save_file_dialog():
     utils.init_qtapp()
     timer = QtCore.QTimer()
diff --git a/skimage/viewer/tests/test_viewer.py b/skimage/viewer/tests/test_viewer.py
index 0709d18d..548565a4 100644
--- a/skimage/viewer/tests/test_viewer.py
+++ b/skimage/viewer/tests/test_viewer.py
@@ -1,11 +1,10 @@
 
 from skimage import data
-try:
-    from skimage.viewer.qt import QtGui, QtCore
-    from skimage.viewer import ImageViewer, CollectionViewer
-    from skimage.viewer.plugins import OverlayPlugin
-except ImportError:
-    ImageViewer = None
+
+from skimage.viewer.qt import QtGui, QtCore, has_qt
+from skimage.viewer import ImageViewer, CollectionViewer
+from skimage.viewer.plugins import OverlayPlugin
+
 from skimage.transform import pyramid_gaussian
 from skimage.filters import sobel
 from numpy.testing import assert_equal
@@ -14,7 +13,7 @@ from skimage._shared.version_requirements import is_installed
 from skimage._shared._warnings import expected_warnings
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_viewer():
     astro = data.astronaut()
     coins = data.coins()
@@ -41,7 +40,7 @@ def make_key_event(key):
                            QtCore.Qt.NoModifier)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_collection_viewer():
 
     img = data.astronaut()
@@ -57,7 +56,7 @@ def test_collection_viewer():
     view._format_coord(10, 10)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 @skipif(not is_installed('matplotlib', '>=1.2'))
 def test_viewer_with_overlay():
     img = data.coins()
diff --git a/skimage/viewer/tests/test_widgets.py b/skimage/viewer/tests/test_widgets.py
index 8e76d29b..66b86fa4 100644
--- a/skimage/viewer/tests/test_widgets.py
+++ b/skimage/viewer/tests/test_widgets.py
@@ -1,14 +1,13 @@
 
 import os
 from skimage import data, img_as_float, io, img_as_uint
-try:
-    from skimage.viewer import ImageViewer
-    from skimage.viewer.qt import QtGui, QtCore
-    from skimage.viewer.widgets import (
-        Slider, OKCancelButtons, SaveButtons, ComboBox, CheckBox, Text)
-    from skimage.viewer.plugins.base import Plugin
-except ImportError:
-    ImageViewer = None
+
+from skimage.viewer import ImageViewer
+from skimage.viewer.qt import QtGui, QtCore, has_qt
+from skimage.viewer.widgets import (
+    Slider, OKCancelButtons, SaveButtons, ComboBox, CheckBox, Text)
+from skimage.viewer.plugins.base import Plugin
+
 from numpy.testing import assert_almost_equal, assert_equal
 from numpy.testing.decorators import skipif
 from skimage._shared._warnings import expected_warnings
@@ -21,7 +20,7 @@ def get_image_viewer():
     return viewer
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_check_box():
     viewer = get_image_viewer()
     cb = CheckBox('hello', value=True, alignment='left')
@@ -36,7 +35,7 @@ def test_check_box():
     assert_equal(cb.val, False)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_combo_box():
     viewer = get_image_viewer()
     cb = ComboBox('hello', ('a', 'b', 'c'))
@@ -49,7 +48,7 @@ def test_combo_box():
     assert_equal(cb.index, 2)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_text_widget():
     viewer = get_image_viewer()
     txt = Text('hello', 'hello, world!')
@@ -60,7 +59,7 @@ def test_text_widget():
     assert_equal(str(txt.text), 'goodbye, world!')
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_slider_int():
     viewer = get_image_viewer()
     sld = Slider('radius', 2, 10, value_type='int')
@@ -74,7 +73,7 @@ def test_slider_int():
     assert_equal(sld.val, 5)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_slider_float():
     viewer = get_image_viewer()
     sld = Slider('alpha', 2.1, 3.1, value=2.1, value_type='float',
@@ -89,7 +88,7 @@ def test_slider_float():
     assert_almost_equal(sld.val, 2.5, 2)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_save_buttons():
     viewer = get_image_viewer()
     sv = SaveButtons()
@@ -117,7 +116,7 @@ def test_save_buttons():
     os.remove(filename)
 
 
-@skipif(ImageViewer is None)
+@skipif(not has_qt)
 def test_ok_buttons():
     viewer = get_image_viewer()
     ok = OKCancelButtons()

From 2eee1faaffa52bcf5cd8cb83692c2e50b7c02b55 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 11:23:46 -0600
Subject: [PATCH 07/17] Fix import error in viewer.utils.core

---
 skimage/viewer/utils/core.py | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/skimage/viewer/utils/core.py b/skimage/viewer/utils/core.py
index dd81d2a7..4f8bfade 100644
--- a/skimage/viewer/utils/core.py
+++ b/skimage/viewer/utils/core.py
@@ -1,17 +1,21 @@
 import warnings
 
 import numpy as np
-from skimage.viewer.qt import QtGui
+from skimage.viewer.qt import QtGui, has_qt
 import matplotlib as mpl
 from matplotlib.figure import Figure
 from matplotlib import _pylab_helpers
 from matplotlib.colors import LinearSegmentedColormap
 
-from matplotlib.backends.backend_qt4 import FigureManagerQT
-from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
-if 'agg' not in mpl.get_backend().lower():
-    warnings.warn("Recommended matplotlib backend is `Agg` for full "
-          "skimage.viewer functionality.")
+if has_qt:
+    from matplotlib.backends.backend_qt4 import FigureManagerQT
+    from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
+    if 'agg' not in mpl.get_backend().lower():
+        warnings.warn("Recommended matplotlib backend is `Agg` for full "
+              "skimage.viewer functionality.")
+else:
+    FigureManagerQT = None
+    FigureCanvasQTAgg = None
 
 
 __all__ = ['init_qtapp', 'start_qtapp', 'RequiredAttr', 'figimage',

From 11c6a9f86a6574a0a38cf26b9b0fa2c61a38e308 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 17:12:00 -0600
Subject: [PATCH 08/17] Fix another viewer import

---
 skimage/viewer/utils/core.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/skimage/viewer/utils/core.py b/skimage/viewer/utils/core.py
index 4f8bfade..517370e1 100644
--- a/skimage/viewer/utils/core.py
+++ b/skimage/viewer/utils/core.py
@@ -14,8 +14,8 @@ if has_qt:
         warnings.warn("Recommended matplotlib backend is `Agg` for full "
               "skimage.viewer functionality.")
 else:
-    FigureManagerQT = None
-    FigureCanvasQTAgg = None
+    FigureManagerQT = object
+    FigureCanvasQTAgg = object
 
 
 __all__ = ['init_qtapp', 'start_qtapp', 'RequiredAttr', 'figimage',

From 6d445776c91d1b6c77e40fdf405fe21146aa7025 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 17:30:15 -0600
Subject: [PATCH 09/17] Fix the dummy Signal

---
 skimage/viewer/qt.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index dc4852c9..9a6537b3 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -14,7 +14,7 @@ except ImportError:
             QWidget = object
 
         class QtCore(object):
-            Signal = object
+            def Signal(*args, **kwargs): pass
             Qt = object
 
         QtWidgets = QtGui

From 7474db1f0d5c1491f852cfea8217656fa866284f Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 19:42:12 -0600
Subject: [PATCH 10/17] Another fix for dummy Signal

---
 skimage/viewer/qt.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index 9a6537b3..b36c15dc 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -14,9 +14,11 @@ except ImportError:
             QWidget = object
 
         class QtCore(object):
-            def Signal(*args, **kwargs): pass
             Qt = object
 
+            def Signal(self, *args, **kwargs): 
+                pass
+
         QtWidgets = QtGui
 
         has_qt = False

From c3ade4416febecb040513a901495f4b61cc08ba9 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 20:55:11 -0600
Subject: [PATCH 11/17] Instantiate QtCore dummy class

---
 skimage/viewer/qt.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index b36c15dc..1d26fbcf 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -13,12 +13,13 @@ except ImportError:
             QDialog = object
             QWidget = object
 
-        class QtCore(object):
+        class QtCore_cls(object):
             Qt = object
 
             def Signal(self, *args, **kwargs): 
                 pass
 
+        QtCore = QtCore_cls()
         QtWidgets = QtGui
 
         has_qt = False

From 8da175d70eaa036909edc8bdac0311163a4ca12a Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 21:20:59 -0600
Subject: [PATCH 12/17] Add dummy Qt properties

---
 skimage/viewer/qt.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index 1d26fbcf..e3880f55 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -14,13 +14,16 @@ except ImportError:
             QWidget = object
 
         class QtCore_cls(object):
-            Qt = object
+            class Qt(object):
+                 TopDockWidgetArea = None
+                 BottomDockWidgetArea = None
+                 LeftDockWidgetArea = None
+                 RightDockWidgetArea = None
 
             def Signal(self, *args, **kwargs): 
                 pass
 
-        QtCore = QtCore_cls()
-        QtWidgets = QtGui
+        QtCore = QtWidgets = QtCore_cls()
 
         has_qt = False
 

From 42b330e5629b25db45e7a0f3f08bdb21e608b106 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 24 Dec 2014 21:40:33 -0600
Subject: [PATCH 13/17] Add QWidget to the mock Qt

---
 skimage/viewer/qt.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index e3880f55..1166b3b6 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -23,6 +23,8 @@ except ImportError:
             def Signal(self, *args, **kwargs): 
                 pass
 
+            QWidget = object
+
         QtCore = QtWidgets = QtCore_cls()
 
         has_qt = False

From 67fadc0ed846a95f6d603827313b555e98985959 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Thu, 25 Dec 2014 17:02:45 -0600
Subject: [PATCH 14/17] Fix mock Qt objects again

---
 skimage/viewer/qt.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index 1166b3b6..240e794c 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -8,7 +8,7 @@ except ImportError:
         QtWidgets = QtGui
     except ImportError:
         # Mock objects
-        class QtGui(object):
+        class QtGui_cls(object):
             QMainWindow = object
             QDialog = object
             QWidget = object
@@ -23,9 +23,8 @@ except ImportError:
             def Signal(self, *args, **kwargs): 
                 pass
 
-            QWidget = object
-
-        QtCore = QtWidgets = QtCore_cls()
+        QtGui = QtWidgets = QtGui_cls()
+        QtCore = QtCore_cls()
 
         has_qt = False
 

From 51ab675d3c6fd67c1f10d218ddc7d9bf04572cb0 Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Sat, 27 Dec 2014 11:11:36 -0600
Subject: [PATCH 15/17] Fix lingering merge issue

---
 skimage/viewer/tests/test_plugins.py | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/skimage/viewer/tests/test_plugins.py b/skimage/viewer/tests/test_plugins.py
index 699578f2..8dcf7855 100644
--- a/skimage/viewer/tests/test_plugins.py
+++ b/skimage/viewer/tests/test_plugins.py
@@ -12,15 +12,7 @@ from skimage.viewer.plugins import (
     PlotPlugin)
 from numpy.testing import assert_equal, assert_allclose, assert_almost_equal
 from numpy.testing.decorators import skipif
-<<<<<<< HEAD
-from skimage.viewer.plugins import (
-    LineProfile, Measure, CannyPlugin, LabelPainter, Crop, ColorHistogram,
-    PlotPlugin)
-from skimage.viewer.plugins.base import Plugin
-from skimage.viewer.widgets import Slider
 from skimage._shared._warnings import expected_warnings
-=======
->>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 
 
 def setup_line_profile(image, limits='image'):

From 14a2b5d8f3f021219ef3ea09c90eeda78f539476 Mon Sep 17 00:00:00 2001
From: Phil Schaf <flying-sheep@web.de>
Date: Tue, 30 Dec 2014 14:20:21 +0100
Subject: [PATCH 16/17] fixed Qt5 compat

---
 skimage/viewer/qt.py         | 16 +++++++++++++---
 skimage/viewer/utils/core.py | 22 ++++++++--------------
 2 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index 240e794c..0f6f5616 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -1,11 +1,10 @@
-has_qt = True
-
 try:
-    from matplotlib.backends.qt_compat import QtGui, QtCore, QtWidgets
+    from matplotlib.backends.qt_compat import QtGui, QtCore, QtWidgets, QT_RC_MAJOR_VERSION as has_qt
 except ImportError:
     try:
         from matplotlib.backends.qt4_compat import QtGui, QtCore
         QtWidgets = QtGui
+        has_qt = 4
     except ImportError:
         # Mock objects
         class QtGui_cls(object):
@@ -28,5 +27,16 @@ except ImportError:
 
         has_qt = False
 
+if has_qt == 5:
+    from matplotlib.backends.backend_qt5 import FigureManagerQT
+    from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg
+elif has_qt == 4:
+    from matplotlib.backends.backend_qt4 import FigureManagerQT
+    from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
+else:
+    assert not has_qt, 'Unsupported Qt version {0}'.format(has_qt)
+    FigureManagerQT = object
+    FigureCanvasQTAgg = object
+
 Qt = QtCore.Qt
 Signal = QtCore.Signal
diff --git a/skimage/viewer/utils/core.py b/skimage/viewer/utils/core.py
index 517370e1..524e9b61 100644
--- a/skimage/viewer/utils/core.py
+++ b/skimage/viewer/utils/core.py
@@ -1,21 +1,15 @@
 import warnings
 
 import numpy as np
-from skimage.viewer.qt import QtGui, has_qt
+from skimage.viewer.qt import QtWidgets, has_qt, FigureManagerQT, FigureCanvasQTAgg
 import matplotlib as mpl
 from matplotlib.figure import Figure
 from matplotlib import _pylab_helpers
 from matplotlib.colors import LinearSegmentedColormap
 
-if has_qt:
-    from matplotlib.backends.backend_qt4 import FigureManagerQT
-    from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
-    if 'agg' not in mpl.get_backend().lower():
-        warnings.warn("Recommended matplotlib backend is `Agg` for full "
-              "skimage.viewer functionality.")
-else:
-    FigureManagerQT = object
-    FigureCanvasQTAgg = object
+if has_qt and 'agg' not in mpl.get_backend().lower():
+    warnings.warn("Recommended matplotlib backend is `Agg` for full "
+                  "skimage.viewer functionality.")
 
 
 __all__ = ['init_qtapp', 'start_qtapp', 'RequiredAttr', 'figimage',
@@ -32,9 +26,9 @@ def init_qtapp():
     The QApplication needs to be initialized before creating any QWidgets
     """
     global QApp
-    QApp = QtGui.QApplication.instance()
+    QApp = QtWidgets.QApplication.instance()
     if QApp is None:
-        QApp = QtGui.QApplication([])
+        QApp = QtWidgets.QApplication([])
     return QApp
 
 
@@ -121,8 +115,8 @@ class FigureCanvas(FigureCanvasQTAgg):
         self.fig = figure
         FigureCanvasQTAgg.__init__(self, self.fig)
         FigureCanvasQTAgg.setSizePolicy(self,
-                                        QtGui.QSizePolicy.Expanding,
-                                        QtGui.QSizePolicy.Expanding)
+                                        QtWidgets.QSizePolicy.Expanding,
+                                        QtWidgets.QSizePolicy.Expanding)
         FigureCanvasQTAgg.updateGeometry(self)
 
     def resizeEvent(self, event):

From d714d0bcbc5ae6928b362c16f8482ec0def5609d Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Tue, 30 Dec 2014 21:01:23 -0600
Subject: [PATCH 17/17] Separate qt version check from has_qt flag

---
 skimage/viewer/qt.py | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index 0f6f5616..8f6768a5 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -1,10 +1,13 @@
+_qt_version = None
+has_qt = True
+
 try:
-    from matplotlib.backends.qt_compat import QtGui, QtCore, QtWidgets, QT_RC_MAJOR_VERSION as has_qt
+    from matplotlib.backends.qt_compat import QtGui, QtCore, QtWidgets, QT_RC_MAJOR_VERSION as _qt_version
 except ImportError:
     try:
         from matplotlib.backends.qt4_compat import QtGui, QtCore
         QtWidgets = QtGui
-        has_qt = 4
+        _qt_version = 4
     except ImportError:
         # Mock objects
         class QtGui_cls(object):
@@ -27,14 +30,13 @@ except ImportError:
 
         has_qt = False
 
-if has_qt == 5:
+if _qt_version == 5:
     from matplotlib.backends.backend_qt5 import FigureManagerQT
     from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg
-elif has_qt == 4:
+elif _qt_version == 4:
     from matplotlib.backends.backend_qt4 import FigureManagerQT
     from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
 else:
-    assert not has_qt, 'Unsupported Qt version {0}'.format(has_qt)
     FigureManagerQT = object
     FigureCanvasQTAgg = object