Make changes re review comments

Make sure __future__ imports are in every file
Use existing context manager to block QSignals
Rename artist_has_errorbars -> artists_workspace_has_errors

Framework/PythonInterface/mantid/plots/__init__.py

@@ -311,8 +311,11 @@ class MantidAxes(Axes):
                 logger.warning("You are overlaying distribution and "
                                "non-distribution data!")
 
-    def artist_has_errorbars(self, artist):
+    def artists_workspace_has_errors(self, artist):
         """Check if the given artist's workspace has errors"""
+        if artist not in self.get_tracked_artists():
+            raise ValueError("Artist '{}' is not tracked and so does not have "
+                             "an associated workspace.".format(artist))
         workspace, spec_num = self.get_artists_workspace_and_spec_num(artist)
         workspace_index = workspace.getIndexFromSpectrumNumber(spec_num)
         if any(workspace.readE(workspace_index) != 0):

qt/python/mantidqt/utils/__init__.py

@@ -23,15 +23,3 @@ class AddedToSysPath:
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         sys.path = self.original_sys_path
-
-
-class BlockQSignals:
-    """Context manager to block QSignals from a QObject"""
-    def __init__(self, qobject):
-        self.qobject = qobject
-
-    def __enter__(self):
-        self.qobject.blockSignals(True)
-
-    def __exit__(self, exc_type, exc_val, exc_tb):
-        self.qobject.blockSignals(False)

qt/python/mantidqt/widgets/plotconfigdialog/__init__.py

@@ -6,6 +6,8 @@
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
 
+from __future__ import (absolute_import, unicode_literals)
+
 from matplotlib.axes import ErrorbarContainer
 from matplotlib.collections import QuadMesh
 

qt/python/mantidqt/widgets/plotconfigdialog/axestabwidget/__init__.py

@@ -6,6 +6,8 @@
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
 
+from __future__ import (absolute_import, unicode_literals)
+
 
 class AxProperties(dict):
     """

qt/python/mantidqt/widgets/plotconfigdialog/curvestabwidget/__init__.py

@@ -6,6 +6,8 @@
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
 
+from __future__ import (absolute_import, unicode_literals)
+
 from matplotlib import rcParams
 from matplotlib.axes import ErrorbarContainer
 from matplotlib.lines import Line2D
@@ -118,12 +120,7 @@ def curve_has_errors(curve):
     ax = get_ax_from_curve(curve)
     if isinstance(ax, MantidAxes):
         try:
-            workspace, spec_num = ax.get_artists_workspace_and_spec_num(curve)
-            workspace_index = workspace.getIndexFromSpectrumNumber(spec_num)
-            if any(workspace.readE(workspace_index) != 0):
-                return True
-            else:
-                return False
+            return ax.artists_workspace_has_errors(curve)
         except ValueError:  # Value error raised if artist has no associated workspace
             return False
     if isinstance(curve, Line2D):

qt/python/mantidqt/widgets/plotconfigdialog/curvestabwidget/errorbarstabwidget/__init__.py

@@ -5,3 +5,5 @@
 #     & Institut Laue - Langevin
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
+
+from __future__ import (absolute_import, unicode_literals)

qt/python/mantidqt/widgets/plotconfigdialog/curvestabwidget/linetabwidget/__init__.py

@@ -5,3 +5,5 @@
 #     & Institut Laue - Langevin
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
+
+from __future__ import (absolute_import, unicode_literals)

qt/python/mantidqt/widgets/plotconfigdialog/curvestabwidget/markertabwidget/__init__.py

@@ -5,3 +5,5 @@
 #     & Institut Laue - Langevin
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
+
+from __future__ import (absolute_import, unicode_literals)

qt/python/mantidqt/widgets/plotconfigdialog/curvestabwidget/presenter.py

@@ -13,7 +13,7 @@ from matplotlib.lines import Line2D
 
 from mantid.plots import MantidAxes
 from mantid.plots.helperfunctions import get_data_from_errorbar_container
-from mantidqt.utils import BlockQSignals
+from mantidqt.utils.qt import block_signals
 from mantidqt.widgets.plotconfigdialog import get_axes_names_dict, curve_in_ax
 from mantidqt.widgets.plotconfigdialog.curvestabwidget import (
     CurveProperties, set_curve_hidden, set_errorbars_hidden, curve_has_errors,
@@ -172,7 +172,7 @@ class CurvesTabWidgetPresenter:
         on the axes remove the axes entry from the 'select_axes_combo_box'. If
         no axes with curves remain close the tab and return True
         """
-        with BlockQSignals(self.view.select_curve_combo_box):
+        with block_signals(self.view.select_curve_combo_box):
             self.view.remove_select_curve_combo_box_selected_item()
             if self.view.select_curve_combo_box.count() == 0:
                 self.view.remove_select_axes_combo_box_selected_item()
@@ -230,7 +230,7 @@ class CurvesTabWidgetPresenter:
         Return False if there are no lines on the axes (this can occur
         when a user uses the "Remove Curve" button), else return True.
         """
-        with BlockQSignals(self.view.select_curve_combo_box):
+        with block_signals(self.view.select_curve_combo_box):
             self.view.select_curve_combo_box.clear()
         selected_ax = self.get_selected_ax()
         if not selected_ax:

qt/python/mantidqt/widgets/plotconfigdialog/curvestabwidget/test/__init__.py

@@ -5,3 +5,5 @@
 #     & Institut Laue - Langevin
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
+
+from __future__ import (absolute_import, unicode_literals)

qt/python/mantidqt/widgets/plotconfigdialog/curvestabwidget/test/test_curvestabwidgetpresenter.py

@@ -6,6 +6,8 @@
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
 
+from __future__ import (absolute_import, unicode_literals)
+
 import unittest
 
 from matplotlib import use as mpl_use

qt/python/mantidqt/widgets/plotconfigdialog/imagestabwidget/presenter.py

@@ -8,7 +8,7 @@
 
 from __future__ import (absolute_import, unicode_literals)
 
-from mantidqt.utils import BlockQSignals
+from mantidqt.utils.qt import block_signals
 from mantidqt.widgets.plotconfigdialog import generate_ax_name, get_images_from_fig
 from mantidqt.widgets.plotconfigdialog.imagestabwidget import ImageProperties
 from mantidqt.widgets.plotconfigdialog.imagestabwidget.view import ImagesTabWidgetView, SCALES
@@ -45,7 +45,7 @@ class ImagesTabWidgetPresenter:
         return self.image_names_dict[self.view.get_selected_image_name()]
 
     def populate_select_image_combo_box_and_update_view(self):
-        with BlockQSignals(self.view.select_image_combo_box):
+        with block_signals(self.view.select_image_combo_box):
             self._populate_select_image_combo_box()
         self.update_view()
 

qt/python/mantidqt/widgets/plotconfigdialog/imagestabwidget/test/__init__.py

@@ -5,3 +5,5 @@
 #     & Institut Laue - Langevin
 # SPDX - License - Identifier: GPL - 3.0 +
 #  This file is part of the mantid workbench.
+
+from __future__ import (absolute_import, unicode_literals)