Cleanup GTK examples.

Right now they emit warnings:
```
gtk_spreadsheet_sgskip.py:36: PyGTKDeprecationWarning: Using positional arguments with the GObject constructor has been deprecated. Please specify keyword(s) for "homogeneous, spacing" or use a class specific constructor. See: https://wiki.gnome.org/PyGObject/InitializerDeprecations
  vbox = Gtk.VBox(False, 8)
gtk_spreadsheet_sgskip.py:39: PyGTKDeprecationWarning: Using positional arguments with the GObject constructor has been deprecated. Please specify keyword(s) for "label" or use a class specific constructor. See: https://wiki.gnome.org/PyGObject/InitializerDeprecations
  label = Gtk.Label('Double click a row to plot the data')
gtk_spreadsheet_sgskip.py:51: PyGTKDeprecationWarning: Using positional arguments with the GObject constructor has been deprecated. Please specify keyword(s) for "model" or use a class specific constructor. See: https://wiki.gnome.org/PyGObject/InitializerDeprecations
  self.treeview = Gtk.TreeView(model)
gtk_spreadsheet_sgskip.py:52: DeprecationWarning: Gtk.TreeView.set_rules_hint is deprecated
  self.treeview.set_rules_hint(True)
```
```
pylab_with_gtk_sgskip.py:30: PyGTKDeprecationWarning: Using positional arguments with the GObject constructor has been deprecated. Please specify keyword(s) for "label" or use a class specific constructor. See: https://wiki.gnome.org/PyGObject/InitializerDeprecations
  button = Gtk.Button('Click me')
```

Fix that, and some more.

Author: anntzer

.flake8

@@ -252,7 +252,7 @@ per-file-ignores =
     examples/user_interfaces/gtk_spreadsheet_sgskip.py: E402
     examples/user_interfaces/mathtext_wx_sgskip.py: E402, E501
     examples/user_interfaces/mpl_with_glade3_sgskip.py: E402
-    examples/user_interfaces/pylab_with_gtk_sgskip.py: E402, E501
+    examples/user_interfaces/pylab_with_gtk_sgskip.py: E302, E402
     examples/user_interfaces/toolmanager_sgskip.py: E402
     examples/userdemo/custom_boxstyle01.py: E402
     examples/userdemo/pgf_preamble_sgskip.py: E402

examples/user_interfaces/gtk_spreadsheet_sgskip.py

@@ -3,55 +3,51 @@
 GTK Spreadsheet
 ===============
 
-Example of embedding matplotlib in an application and interacting with
-a treeview to store data.  Double click on an entry to update plot
-data
-
+Example of embedding Matplotlib in an application and interacting with a
+treeview to store data.  Double click on an entry to update plot data.
 """
+
 import gi
 gi.require_version('Gtk', '3.0')
 gi.require_version('Gdk', '3.0')
 from gi.repository import Gtk, Gdk
 
-from matplotlib.backends.backend_gtk3agg import FigureCanvas
-# from matplotlib.backends.backend_gtk3cairo import FigureCanvas
+from matplotlib.backends.backend_gtk3agg import FigureCanvas  # or gtk3cairo.
 
 from numpy.random import random
 from matplotlib.figure import Figure
 
 
 class DataManager(Gtk.Window):
-    numRows, numCols = 20, 10
+    num_rows, num_cols = 20, 10
 
-    data = random((numRows, numCols))
+    data = random((num_rows, num_cols))
 
     def __init__(self):
-        Gtk.Window.__init__(self)
+        super().__init__()
         self.set_default_size(600, 600)
         self.connect('destroy', lambda win: Gtk.main_quit())
 
         self.set_title('GtkListStore demo')
         self.set_border_width(8)
 
-        vbox = Gtk.VBox(False, 8)
+        vbox = Gtk.VBox(homogeneous=False, spacing=8)
         self.add(vbox)
 
-        label = Gtk.Label('Double click a row to plot the data')
+        label = Gtk.Label(label='Double click a row to plot the data')
 
         vbox.pack_start(label, False, False, 0)
 
         sw = Gtk.ScrolledWindow()
         sw.set_shadow_type(Gtk.ShadowType.ETCHED_IN)
-        sw.set_policy(Gtk.PolicyType.NEVER,
-                      Gtk.PolicyType.AUTOMATIC)
+        sw.set_policy(Gtk.PolicyType.NEVER, Gtk.PolicyType.AUTOMATIC)
         vbox.pack_start(sw, True, True, 0)
 
         model = self.create_model()
 
-        self.treeview = Gtk.TreeView(model)
-        self.treeview.set_rules_hint(True)
+        self.treeview = Gtk.TreeView(model=model)
 
-        # matplotlib stuff
+        # Matplotlib stuff
         fig = Figure(figsize=(6, 4))
 
         self.canvas = FigureCanvas(fig)  # a Gtk.DrawingArea
@@ -75,14 +71,13 @@ def plot_row(self, treeview, path, view_column):
         self.canvas.draw()
 
     def add_columns(self):
-        for i in range(self.numCols):
+        for i in range(self.num_cols):
             column = Gtk.TreeViewColumn(str(i), Gtk.CellRendererText(), text=i)
             self.treeview.append_column(column)
 
     def create_model(self):
-        types = [float]*self.numCols
+        types = [float] * self.num_cols
         store = Gtk.ListStore(*types)
-
         for row in self.data:
             store.append(tuple(row))
         return store

examples/user_interfaces/pylab_with_gtk_sgskip.py

@@ -1,62 +1,58 @@
 """
 ===============
-Pyplot With GTK
+pyplot with GTK
 ===============
 
-An example of how to use pyplot to manage your figure windows, but
-modify the GUI by accessing the underlying gtk widgets
+An example of how to use pyplot to manage your figure windows, but modify the
+GUI by accessing the underlying GTK widgets.
 """
+
 import matplotlib
 matplotlib.use('GTK3Agg')  # or 'GTK3Cairo'
 import matplotlib.pyplot as plt
 
+import gi
+gi.require_version('Gtk', '3.0')
+from gi.repository import Gtk
 
-fig, ax = plt.subplots()
-plt.plot([1, 2, 3], 'ro-', label='easy as 1 2 3')
-plt.plot([1, 4, 9], 'gs--', label='easy as 1 2 3 squared')
-plt.legend()
 
+fig, ax = plt.subplots()
+ax.plot([1, 2, 3], 'ro-', label='easy as 1 2 3')
+ax.plot([1, 4, 9], 'gs--', label='easy as 1 2 3 squared')
+ax.legend()
 
-manager = plt.get_current_fig_manager()
-# you can also access the window or vbox attributes this way
+manager = fig.canvas.manager
+# you can access the window or vbox attributes this way
 toolbar = manager.toolbar
+vbox = manager.vbox
 
 # now let's add a button to the toolbar
-import gi
-gi.require_version('Gtk', '3.0')
-from gi.repository import Gtk
-pos = 8  # where to insert this in the mpl toolbar
-button = Gtk.Button('Click me')
+button = Gtk.Button(label='Click me')
 button.show()
-
-
-def clicked(button):
-    print('hi mom')
-button.connect('clicked', clicked)
+button.connect('clicked', lambda button: print('hi mom'))
 
 toolitem = Gtk.ToolItem()
 toolitem.show()
 toolitem.set_tooltip_text('Click me for fun and profit')
-
 toolitem.add(button)
+
+pos = 8  # where to insert this in the mpl toolbar
 toolbar.insert(toolitem, pos)
-pos += 1
 
 # now let's add a widget to the vbox
 label = Gtk.Label()
 label.set_markup('Drag mouse over axes for position')
 label.show()
-vbox = manager.vbox
 vbox.pack_start(label, False, False, 0)
-vbox.reorder_child(manager.toolbar, -1)
-
+vbox.reorder_child(toolbar, -1)
 
 def update(event):
     if event.xdata is None:
         label.set_markup('Drag mouse over axes for position')
     else:
-        label.set_markup('<span color="#ef0000">x,y=(%f, %f)</span>' % (event.xdata, event.ydata))
+        label.set_markup(
+            f'<span color="#ef0000">x,y=({event.xdata}, {event.ydata})</span>')
 
-plt.connect('motion_notify_event', update)
+fig.canvas.mpl_connect('motion_notify_event', update)
 
 plt.show()