diff --git a/doc/sphinxext/github.py b/doc/sphinxext/github.py
index 75c5ce10ae9d..d0b586256b9f 100644
--- a/doc/sphinxext/github.py
+++ b/doc/sphinxext/github.py
@@ -103,7 +103,6 @@ def ghuser_role(name, rawtext, text, lineno, inliner, options={}, content=[]):
     :param options: Directive options for customization.
     :param content: The directive content for customization.
     """
-    app = inliner.document.settings.env.app
     ref = 'https://www.github.com/' + text
     node = nodes.reference(rawtext, text, refuri=ref, **options)
     return [node], []
diff --git a/examples/axes_grid1/demo_axes_grid.py b/examples/axes_grid1/demo_axes_grid.py
index b21b288c355e..9cf356a1ba93 100644
--- a/examples/axes_grid1/demo_axes_grid.py
+++ b/examples/axes_grid1/demo_axes_grid.py
@@ -28,13 +28,10 @@ def demo_simple_grid(fig):
                      axes_pad=0.05,
                      label_mode="1",
                      )
-
     Z, extent = get_demo_image()
     for ax in grid:
-        im = ax.imshow(Z, extent=extent, interpolation="nearest")
-
-    # This only affects axes in first column and second row as share_all =
-    # False.
+        ax.imshow(Z, extent=extent, interpolation="nearest")
+    # This only affects axes in first column and second row as share_all=False.
     grid.axes_llc.set_xticks([-2, 0, 2])
     grid.axes_llc.set_yticks([-2, 0, 2])
 
diff --git a/examples/axes_grid1/demo_edge_colorbar.py b/examples/axes_grid1/demo_edge_colorbar.py
index 313790a9edfc..6603d5bb263a 100644
--- a/examples/axes_grid1/demo_edge_colorbar.py
+++ b/examples/axes_grid1/demo_edge_colorbar.py
@@ -41,7 +41,7 @@ def demo_bottom_cbar(fig):
         im = grid[i].imshow(Z, extent=extent, interpolation="nearest",
                             cmap=cmaps[i//2])
         if i % 2:
-            cbar = grid.cbar_axes[i//2].colorbar(im)
+            grid.cbar_axes[i//2].colorbar(im)
 
     for cax in grid.cbar_axes:
         cax.toggle_label(True)
diff --git a/examples/event_handling/pick_event_demo.py b/examples/event_handling/pick_event_demo.py
index 31b52cf4bed8..ad004abf3fa2 100644
--- a/examples/event_handling/pick_event_demo.py
+++ b/examples/event_handling/pick_event_demo.py
@@ -83,7 +83,7 @@ def pick_simple():
     line, = ax1.plot(rand(100), 'o', picker=5)  # 5 points tolerance
 
     # pick the rectangle
-    bars = ax2.bar(range(10), rand(10), picker=True)
+    ax2.bar(range(10), rand(10), picker=True)
     for label in ax2.get_xticklabels():  # make the xtick labels pickable
         label.set_picker(True)
 
@@ -157,18 +157,17 @@ def onpick3(event):
         print('onpick3 scatter:', ind, x[ind], y[ind])
 
     fig, ax = plt.subplots()
-    col = ax.scatter(x, y, 100*s, c, picker=True)
-    #fig.savefig('pscoll.eps')
+    ax.scatter(x, y, 100*s, c, picker=True)
     fig.canvas.mpl_connect('pick_event', onpick3)
 
 
 def pick_image():
     # picking images (matplotlib.image.AxesImage)
     fig, ax = plt.subplots()
-    im1 = ax.imshow(rand(10, 5), extent=(1, 2, 1, 2), picker=True)
-    im2 = ax.imshow(rand(5, 10), extent=(3, 4, 1, 2), picker=True)
-    im3 = ax.imshow(rand(20, 25), extent=(1, 2, 3, 4), picker=True)
-    im4 = ax.imshow(rand(30, 12), extent=(3, 4, 3, 4), picker=True)
+    ax.imshow(rand(10, 5), extent=(1, 2, 1, 2), picker=True)
+    ax.imshow(rand(5, 10), extent=(3, 4, 1, 2), picker=True)
+    ax.imshow(rand(20, 25), extent=(1, 2, 3, 4), picker=True)
+    ax.imshow(rand(30, 12), extent=(3, 4, 3, 4), picker=True)
     ax.axis([0, 5, 0, 5])
 
     def onpick4(event):
diff --git a/examples/misc/demo_agg_filter.py b/examples/misc/demo_agg_filter.py
index 8e638688a71d..a8e61de383de 100644
--- a/examples/misc/demo_agg_filter.py
+++ b/examples/misc/demo_agg_filter.py
@@ -187,8 +187,8 @@ def filtered_text(ax):
     Z = (Z1 - Z2) * 2
 
     # draw
-    im = ax.imshow(Z, interpolation='bilinear', origin='lower',
-                   cmap=cm.gray, extent=(-3, 3, -2, 2))
+    ax.imshow(Z, interpolation='bilinear', origin='lower',
+              cmap=cm.gray, extent=(-3, 3, -2, 2))
     levels = np.arange(-1.2, 1.6, 0.2)
     CS = ax.contour(Z, levels,
                     origin='lower',
diff --git a/examples/units/basic_units.py b/examples/units/basic_units.py
index 50ca20675c5b..56ca528162c8 100644
--- a/examples/units/basic_units.py
+++ b/examples/units/basic_units.py
@@ -25,9 +25,7 @@ def __get__(self, obj, objtype=None):
 class TaggedValueMeta(type):
     def __init__(self, name, bases, dict):
         for fn_name in self._proxies:
-            try:
-                dummy = getattr(self, fn_name)
-            except AttributeError:
+            if not hasattr(self, fn_name):
                 setattr(self, fn_name,
                         ProxyDelegate(fn_name, self._proxies[fn_name]))
 
diff --git a/examples/widgets/menu.py b/examples/widgets/menu.py
index 326e28fd81a1..21fa00edbdaa 100644
--- a/examples/widgets/menu.py
+++ b/examples/widgets/menu.py
@@ -132,8 +132,6 @@ def __init__(self, fig, menuitems):
         maxw = max(item.labelwidth for item in menuitems)
         maxh = max(item.labelheight for item in menuitems)
 
-        totalh = self.numitems*maxh + (self.numitems + 1)*2*MenuItem.pady
-
         x0 = 100
         y0 = 400
 
diff --git a/lib/matplotlib/axes/_secondary_axes.py b/lib/matplotlib/axes/_secondary_axes.py
index b5b4598439c6..3f0766fb3058 100644
--- a/lib/matplotlib/axes/_secondary_axes.py
+++ b/lib/matplotlib/axes/_secondary_axes.py
@@ -295,16 +295,14 @@ def _set_lims(self):
         if self._orientation == 'x':
             lims = self._parent.get_xlim()
             set_lim = self.set_xlim
-            trans = self.xaxis.get_transform()
         if self._orientation == 'y':
             lims = self._parent.get_ylim()
             set_lim = self.set_ylim
-            trans = self.yaxis.get_transform()
         order = lims[0] < lims[1]
         lims = self._functions[0](np.array(lims))
         neworder = lims[0] < lims[1]
         if neworder != order:
-            # flip because the transform will take care of the flipping..
+            # Flip because the transform will take care of the flipping.
             lims = lims[::-1]
         set_lim(lims)
 
diff --git a/lib/matplotlib/backends/backend_gtk3.py b/lib/matplotlib/backends/backend_gtk3.py
index 9f6d1f693c29..77df07a2733b 100644
--- a/lib/matplotlib/backends/backend_gtk3.py
+++ b/lib/matplotlib/backends/backend_gtk3.py
@@ -235,7 +235,7 @@ def motion_notify_event(self, widget, event):
         if event.is_hint:
             t, x, y, state = event.window.get_pointer()
         else:
-            x, y, state = event.x, event.y, event.get_state()
+            x, y = event.x, event.y
 
         # flipy so y=0 is bottom of canvas
         y = self.get_allocation().height - y
@@ -582,7 +582,8 @@ def configure_subplots(self, button):
         toolfig = Figure(figsize=(6, 3))
         canvas = self._get_canvas(toolfig)
         toolfig.subplots_adjust(top=0.9)
-        tool = SubplotTool(self.canvas.figure, toolfig)
+        # Need to keep a reference to the tool.
+        _tool = SubplotTool(self.canvas.figure, toolfig)
 
         w = int(toolfig.bbox.width)
         h = int(toolfig.bbox.height)
diff --git a/lib/matplotlib/backends/backend_gtk3agg.py b/lib/matplotlib/backends/backend_gtk3agg.py
index 8e5b991daf80..82ba6ef1cc9e 100644
--- a/lib/matplotlib/backends/backend_gtk3agg.py
+++ b/lib/matplotlib/backends/backend_gtk3agg.py
@@ -61,9 +61,8 @@ def blit(self, bbox=None):
             bbox = self.figure.bbox
 
         allocation = self.get_allocation()
-        w, h = allocation.width, allocation.height
         x = int(bbox.x0)
-        y = h - int(bbox.y1)
+        y = allocation.height - int(bbox.y1)
         width = int(bbox.x1) - int(bbox.x0)
         height = int(bbox.y1) - int(bbox.y0)
 
diff --git a/lib/matplotlib/backends/backend_macosx.py b/lib/matplotlib/backends/backend_macosx.py
index f88bf2bb8edc..ca32842ae55a 100644
--- a/lib/matplotlib/backends/backend_macosx.py
+++ b/lib/matplotlib/backends/backend_macosx.py
@@ -160,7 +160,8 @@ def prepare_configure_subplots(self):
         toolfig = Figure(figsize=(6, 3))
         canvas = FigureCanvasMac(toolfig)
         toolfig.subplots_adjust(top=0.9)
-        tool = SubplotTool(self.canvas.figure, toolfig)
+        # Need to keep a reference to the tool.
+        _tool = SubplotTool(self.canvas.figure, toolfig)
         return canvas
 
     def set_message(self, message):
diff --git a/lib/matplotlib/backends/backend_svg.py b/lib/matplotlib/backends/backend_svg.py
index 220ece3911e2..6cdc3ffd7594 100644
--- a/lib/matplotlib/backends/backend_svg.py
+++ b/lib/matplotlib/backends/backend_svg.py
@@ -1026,15 +1026,10 @@ def _draw_text_as_text(self, gc, x, y, s, prop, angle, ismath, mtext=None):
             font = self._get_font(prop)
             font.set_text(s, 0.0, flags=LOAD_NO_HINTING)
 
-            fontsize = prop.get_size_in_points()
-
-            fontfamily = font.family_name
-            fontstyle = prop.get_style()
-
             attrib = {}
             # Must add "px" to workaround a Firefox bug
-            style['font-size'] = short_float_fmt(fontsize) + 'px'
-            style['font-family'] = str(fontfamily)
+            style['font-size'] = short_float_fmt(prop.get_size()) + 'px'
+            style['font-family'] = str(font.family_name)
             style['font-style'] = prop.get_style().lower()
             style['font-weight'] = str(prop.get_weight()).lower()
             attrib['style'] = generate_css(style)
diff --git a/lib/matplotlib/cbook/deprecation.py b/lib/matplotlib/cbook/deprecation.py
index c3393fc84a80..8920e55044fc 100644
--- a/lib/matplotlib/cbook/deprecation.py
+++ b/lib/matplotlib/cbook/deprecation.py
@@ -394,9 +394,7 @@ def _make_keyword_only(since, name, func=None):
     kwonly = [name for name in names[names.index(name):]
               if signature.parameters[name].kind == POK]
     func.__signature__ = signature.replace(parameters=[
-        param.replace(kind=inspect.Parameter.KEYWORD_ONLY)
-        if param.name in kwonly
-        else param
+        param.replace(kind=KWO) if param.name in kwonly else param
         for param in signature.parameters.values()])
 
     @functools.wraps(func)
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
index ab2a40bda23b..049cdfeef7bc 100644
--- a/lib/matplotlib/collections.py
+++ b/lib/matplotlib/collections.py
@@ -1497,7 +1497,6 @@ def get_positions(self):
         '''
         return an array containing the floating-point values of the positions
         '''
-        segments = self.get_segments()
         pos = 0 if self.is_horizontal() else 1
         return [segment[0, pos] for segment in self.get_segments()]
 
diff --git a/lib/matplotlib/colorbar.py b/lib/matplotlib/colorbar.py
index cc873c26cc9f..9372a66eaa5b 100644
--- a/lib/matplotlib/colorbar.py
+++ b/lib/matplotlib/colorbar.py
@@ -596,14 +596,9 @@ def update_ticks(self):
         called whenever the tick locator and/or tick formatter changes.
         """
         ax = self.ax
-        # get the locator and formatter.  Defaults to
-        # self.locator if not None..
+        # Get the locator and formatter; defaults to self.locator if not None.
         locator, formatter = self._get_ticker_locator_formatter()
-        if self.orientation == 'vertical':
-            long_axis, short_axis = ax.yaxis, ax.xaxis
-        else:
-            long_axis, short_axis = ax.xaxis, ax.yaxis
-
+        long_axis = ax.yaxis if self.orientation == 'vertical' else ax.xaxis
         if self._use_auto_colorbar_locator():
             _log.debug('Using auto colorbar locator on colorbar')
             _log.debug('locator: %r', locator)
@@ -643,10 +638,8 @@ def get_ticks(self, minor=False):
         """Return the x ticks as a list of locations."""
         if self._manual_tick_data_values is None:
             ax = self.ax
-            if self.orientation == 'vertical':
-                long_axis, short_axis = ax.yaxis, ax.xaxis
-            else:
-                long_axis, short_axis = ax.xaxis, ax.yaxis
+            long_axis = (
+                ax.yaxis if self.orientation == 'vertical' else ax.xaxis)
             return long_axis.get_majorticklocs()
         else:
             # We made the axes manually, the old way, and the ylim is 0-1,
diff --git a/lib/matplotlib/dviread.py b/lib/matplotlib/dviread.py
index d77d8a50b54e..e1f40be2841f 100644
--- a/lib/matplotlib/dviread.py
+++ b/lib/matplotlib/dviread.py
@@ -455,7 +455,7 @@ def _fnt_def_real(self, k, c, s, d, a, l):
 
     @_dispatch(247, state=_dvistate.pre, args=('u1', 'u4', 'u4', 'u4', 'u1'))
     def _pre(self, i, num, den, mag, k):
-        comment = self.file.read(k)
+        self.file.read(k)  # comment in the dvi file
         if i != 2:
             raise ValueError("Unknown dvi format %d" % i)
         if num != 25400000 or den != 7227 * 2**16:
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
index ea707a3068a8..ad68ef23a4fa 100644
--- a/lib/matplotlib/rcsetup.py
+++ b/lib/matplotlib/rcsetup.py
@@ -965,7 +965,7 @@ def validate_webagg_address(s):
         import socket
         try:
             socket.inet_aton(s)
-        except socket.error as e:
+        except socket.error:
             raise ValueError("'webagg.address' is not a valid IP address")
         return s
     raise ValueError("'webagg.address' is not a valid IP address")
diff --git a/lib/matplotlib/sphinxext/plot_directive.py b/lib/matplotlib/sphinxext/plot_directive.py
index 5b8f15fd5f49..58570c263716 100644
--- a/lib/matplotlib/sphinxext/plot_directive.py
+++ b/lib/matplotlib/sphinxext/plot_directive.py
@@ -518,7 +518,7 @@ def run_code(code, code_path, ns=None, function_name=None):
                 if function_name is not None:
                     exec(function_name + "()", ns)
 
-        except (Exception, SystemExit) as err:
+        except (Exception, SystemExit):
             raise PlotError(traceback.format_exc())
         finally:
             os.chdir(pwd)
@@ -584,11 +584,11 @@ def render_figures(code, code_path, output_dir, output_base, context,
                                 output_dir)
             else:
                 img = ImageFile('%s_%02d' % (output_base, j), output_dir)
-            for format, dpi in formats:
-                if out_of_date(code_path, img.filename(format)):
+            for fmt, dpi in formats:
+                if out_of_date(code_path, img.filename(fmt)):
                     all_exists = False
                     break
-                img.formats.append(format)
+                img.formats.append(fmt)
 
             # assume that if we have one, we have them all
             if not all_exists:
@@ -636,12 +636,12 @@ def render_figures(code, code_path, output_dir, output_base, context,
                 img = ImageFile("%s_%02d_%02d" % (output_base, i, j),
                                 output_dir)
             images.append(img)
-            for format, dpi in formats:
+            for fmt, dpi in formats:
                 try:
-                    figman.canvas.figure.savefig(img.filename(format), dpi=dpi)
-                except Exception as err:
+                    figman.canvas.figure.savefig(img.filename(fmt), dpi=dpi)
+                except Exception:
                     raise PlotError(traceback.format_exc())
-                img.formats.append(format)
+                img.formats.append(fmt)
 
         results.append((code_piece, images))
 
diff --git a/lib/matplotlib/texmanager.py b/lib/matplotlib/texmanager.py
index 8b9840341bf5..0b1773bd5648 100644
--- a/lib/matplotlib/texmanager.py
+++ b/lib/matplotlib/texmanager.py
@@ -227,7 +227,7 @@ def make_tex(self, tex, fontsize):
             else:
                 try:
                     fh.write(s.encode('ascii'))
-                except UnicodeEncodeError as err:
+                except UnicodeEncodeError:
                     _log.info("You are using unicode and latex, but have not "
                               "enabled the 'text.latex.unicode' rcParam.")
                     raise
@@ -289,7 +289,7 @@ def make_tex_preview(self, tex, fontsize):
             else:
                 try:
                     fh.write(s.encode('ascii'))
-                except UnicodeEncodeError as err:
+                except UnicodeEncodeError:
                     _log.info("You are using unicode and latex, but have not "
                               "enabled the 'text.latex.unicode' rcParam.")
                     raise
diff --git a/lib/matplotlib/textpath.py b/lib/matplotlib/textpath.py
index ae289f35f8f6..8122f24644c5 100644
--- a/lib/matplotlib/textpath.py
+++ b/lib/matplotlib/textpath.py
@@ -254,7 +254,7 @@ def get_glyphs_mathtext(self, prop, s, glyph_map=None,
             if char_id not in glyph_map:
                 font.clear()
                 font.set_size(self.FONT_SCALE, self.DPI)
-                glyph = font.load_char(ccode, flags=LOAD_NO_HINTING)
+                font.load_char(ccode, flags=LOAD_NO_HINTING)
                 glyph_map_new[char_id] = font.get_path()
 
             xpositions.append(ox)
@@ -371,9 +371,9 @@ def _get_ps_font_and_encoding(texname):
             # FreeType-synthesized charmap but the native ones (we can't
             # directly identify it but it's typically an Adobe charmap), and
             # directly load the dvi glyph indices using FT_Load_Char/load_char.
-            for charmap_name, charmap_code in [
-                    ("ADOBE_CUSTOM", 1094992451),
-                    ("ADOBE_STANDARD", 1094995778),
+            for charmap_code in [
+                    1094992451,  # ADOBE_CUSTOM.
+                    1094995778,  # ADOBE_STANDARD.
             ]:
                 try:
                     font.select_charmap(charmap_code)
@@ -382,7 +382,6 @@ def _get_ps_font_and_encoding(texname):
                 else:
                     break
             else:
-                charmap_name = ""
                 _log.warning("No supported encoding in font (%s).",
                              font_bunch.filename)
             enc = None
diff --git a/lib/mpl_toolkits/axes_grid1/axes_size.py b/lib/mpl_toolkits/axes_grid1/axes_size.py
index 4edc50d323fc..112843c95ce6 100644
--- a/lib/mpl_toolkits/axes_grid1/axes_size.py
+++ b/lib/mpl_toolkits/axes_grid1/axes_size.py
@@ -111,7 +111,7 @@ def get_size(self, renderer):
         l1, l2 = self._axes.get_xlim()
         if self._aspect == "axes":
             ref_aspect = _get_axes_aspect(self._ref_ax)
-            aspect = ref_aspect/_get_axes_aspect(self._axes)
+            aspect = ref_aspect / _get_axes_aspect(self._axes)
         else:
             aspect = self._aspect
 
diff --git a/lib/mpl_toolkits/axes_grid1/colorbar.py b/lib/mpl_toolkits/axes_grid1/colorbar.py
index d12cc1dc4bf1..cb2bc8edea21 100644
--- a/lib/mpl_toolkits/axes_grid1/colorbar.py
+++ b/lib/mpl_toolkits/axes_grid1/colorbar.py
@@ -788,7 +788,7 @@ def on_changed(m):
         cb.set_clim(m.get_clim())
         cb.update_bruteforce(m)
 
-    cbid = mappable.callbacksSM.connect('changed', on_changed)
+    mappable.callbacksSM.connect('changed', on_changed)
     mappable.colorbar = cb
     ax.figure.sca(ax)
     return cb
diff --git a/lib/mpl_toolkits/axisartist/angle_helper.py b/lib/mpl_toolkits/axisartist/angle_helper.py
index 58c0772c6f10..a4423f6367df 100644
--- a/lib/mpl_toolkits/axisartist/angle_helper.py
+++ b/lib/mpl_toolkits/axisartist/angle_helper.py
@@ -108,15 +108,16 @@ def select_step(v1, v2, nv, hour=False, include_last=True,
         cycle = 360.
 
     # for degree
-    if dv > 1./threshold_factor:
+    if dv > 1 / threshold_factor:
         step, factor = _select_step(dv)
     else:
         step, factor = select_step_sub(dv*threshold_factor)
 
         factor = factor * threshold_factor
 
-    f1, f2, fstep = v1*factor, v2*factor, step/factor
-    levs = np.arange(np.floor(f1/step), np.ceil(f2/step)+0.5, dtype=int) * step
+    levs = np.arange(np.floor(v1 * factor / step),
+                     np.ceil(v2 * factor / step) + 0.5,
+                     dtype=int) * step
 
     # n : number of valid levels. If there is a cycle, e.g., [0, 90, 180,
     # 270, 360], the grid line needs to be extended from 0 to 360, so
@@ -128,7 +129,7 @@ def select_step(v1, v2, nv, hour=False, include_last=True,
     # we need to check the range of values
     # for example, -90 to 90, 0 to 360,
 
-    if factor == 1. and levs[-1] >= levs[0]+cycle:  # check for cycle
+    if factor == 1. and levs[-1] >= levs[0] + cycle:  # check for cycle
         nv = int(cycle / step)
         if include_last:
             levs = levs[0] + np.arange(0, nv+1, 1) * step
diff --git a/lib/mpl_toolkits/axisartist/axis_artist.py b/lib/mpl_toolkits/axisartist/axis_artist.py
index 2a6ca8fe4756..657adbc25776 100644
--- a/lib/mpl_toolkits/axisartist/axis_artist.py
+++ b/lib/mpl_toolkits/axisartist/axis_artist.py
@@ -1194,10 +1194,6 @@ def _draw_label2(self, renderer):
         if not self.label.get_visible():
             return
 
-        fontprops = font_manager.FontProperties(
-            size=rcParams['axes.labelsize'],
-            weight=rcParams['axes.labelweight'])
-
         if self._ticklabel_add_angle != self._axislabel_add_angle:
             if ((self.major_ticks.get_visible()
                  and not self.major_ticks.get_tick_out())