diff --git a/examples/GLIsosurface.py b/examples/GLIsosurface.py
index 0f773885..1afe797c 100644
--- a/examples/GLIsosurface.py
+++ b/examples/GLIsosurface.py
@@ -8,7 +8,6 @@ This example uses the isosurface function to convert a scalar field
 import initExample
 
 import numpy as np
-from pyqtgraph.Qt import QtCore, QtGui
 import pyqtgraph as pg
 import pyqtgraph.opengl as gl
 
@@ -29,7 +28,6 @@ def psi(i, j, k, offset=(25, 25, 50)):
     y = j-offset[1]
     z = k-offset[2]
     th = np.arctan2(z, np.hypot(x, y))
-    phi = np.arctan2(y, x)
     r = np.sqrt(x**2 + y**2 + z **2)
     a0 = 1
     ps = (1./81.) * 1./(6.*np.pi)**0.5 * (1./a0)**(3/2) * (r/a0)**2 * np.exp(-r/(3*a0)) * (3 * np.cos(th)**2 - 1)
diff --git a/examples/GLVolumeItem.py b/examples/GLVolumeItem.py
index 99856a00..ba67514b 100644
--- a/examples/GLVolumeItem.py
+++ b/examples/GLVolumeItem.py
@@ -9,7 +9,6 @@ import initExample
 
 import numpy as np
 import pyqtgraph as pg
-from pyqtgraph.Qt import QtCore, QtGui
 import pyqtgraph.opengl as gl
 from pyqtgraph import functions as fn
 
@@ -31,10 +30,8 @@ def psi(i, j, k, offset=(50,50,100)):
     y = j-offset[1]
     z = k-offset[2]
     th = np.arctan2(z, np.hypot(x, y))
-    phi = np.arctan2(y, x)
     r = np.sqrt(x**2 + y**2 + z **2)
     a0 = 2
-    #ps = (1./81.) * (2./np.pi)**0.5 * (1./a0)**(3/2) * (6 - r/a0) * (r/a0) * np.exp(-r/(3*a0)) * np.cos(th)
     ps = (1./81.) * 1./(6.*np.pi)**0.5 * (1./a0)**(3/2) * (r/a0)**2 * np.exp(-r/(3*a0)) * (3 * np.cos(th)**2 - 1)
     return ps
 
diff --git a/pyqtgraph/Point.py b/pyqtgraph/Point.py
index 6f56a035..bdd8bc33 100644
--- a/pyqtgraph/Point.py
+++ b/pyqtgraph/Point.py
@@ -8,6 +8,7 @@ Distributed under MIT/X11 license. See license.txt for more information.
 from .Qt import QtCore
 from math import atan2, hypot, degrees
 
+
 class Point(QtCore.QPointF):
     """Extension of QPointF which adds a few missing methods."""
     
diff --git a/pyqtgraph/Vector.py b/pyqtgraph/Vector.py
index 2c838d64..a64e8968 100644
--- a/pyqtgraph/Vector.py
+++ b/pyqtgraph/Vector.py
@@ -7,7 +7,6 @@ Distributed under MIT/X11 license. See license.txt for more information.
 from math import acos, degrees
 from .Qt import QtGui, QtCore, QT_LIB
 from . import functions as fn
-import numpy as np
 
 class Vector(QtGui.QVector3D):
     """Extension of QVector3D which adds a few helpful methods."""
diff --git a/pyqtgraph/canvas/CanvasItem.py b/pyqtgraph/canvas/CanvasItem.py
index 0cd86d0e..3883919e 100644
--- a/pyqtgraph/canvas/CanvasItem.py
+++ b/pyqtgraph/canvas/CanvasItem.py
@@ -1,6 +1,5 @@
 # -*- coding: utf-8 -*-
-import numpy as np
-from ..Qt import QtGui, QtCore, QtSvg, QT_LIB
+from ..Qt import QtGui, QtCore, QT_LIB
 from .. import functions as fn
 from ..graphicsItems.ROI import ROI
 from .. import SRTTransform, ItemGroup
diff --git a/pyqtgraph/functions.py b/pyqtgraph/functions.py
index abbd77d1..45043a4c 100644
--- a/pyqtgraph/functions.py
+++ b/pyqtgraph/functions.py
@@ -67,10 +67,8 @@ def siScale(x, minVal=1e-25, allowUnicode=True):
         raise
     if abs(x) < minVal:
         m = 0
-        x = 0
     else:
         m = int(clip_scalar(math.floor(math.log(abs(x))/math.log(1000)), -9.0, 9.0))
-    
     if m == 0:
         pref = ''
     elif m < -8 or m > 8:
@@ -82,7 +80,6 @@ def siScale(x, minVal=1e-25, allowUnicode=True):
             pref = SI_PREFIXES_ASCII[m+8]
     m1 = -3*m
     p = 10.**m1
-    
     return (p, pref)
 
 
diff --git a/pyqtgraph/graphicsItems/CurvePoint.py b/pyqtgraph/graphicsItems/CurvePoint.py
index 66117165..c7052ddb 100644
--- a/pyqtgraph/graphicsItems/CurvePoint.py
+++ b/pyqtgraph/graphicsItems/CurvePoint.py
@@ -2,7 +2,6 @@ from math import atan2, degrees
 from ..Qt import QtGui, QtCore
 from . import ArrowItem
 from ..functions import clip_scalar
-import numpy as np
 from ..Point import Point
 import weakref
 from .GraphicsObject import GraphicsObject
diff --git a/pyqtgraph/graphicsItems/ROI.py b/pyqtgraph/graphicsItems/ROI.py
index 08ff0480..6c5f8418 100644
--- a/pyqtgraph/graphicsItems/ROI.py
+++ b/pyqtgraph/graphicsItems/ROI.py
@@ -15,9 +15,9 @@ of how to build an ROI at the bottom of the file.
 from ..Qt import QtCore, QtGui
 import numpy as np
 #from numpy.linalg import norm
-from ..Point import *
+from ..Point import Point
 from ..SRTTransform import SRTTransform
-from math import atan2, cos, sin, hypot, radians, degrees
+from math import atan2, cos, sin, hypot, radians
 from .. import functions as fn
 from .GraphicsObject import GraphicsObject
 from .UIGraphicsItem import UIGraphicsItem
@@ -141,12 +141,13 @@ class ROI(GraphicsObject):
                  maxBounds=None, snapSize=1.0, scaleSnap=False,
                  translateSnap=False, rotateSnap=False, parent=None, pen=None,
                  hoverPen=None, handlePen=None, handleHoverPen=None,
-                 movable=True, rotatable=True, resizable=True, removable=False):
+                 movable=True, rotatable=True, resizable=True, removable=False,
+                 aspectLocked=False):
         GraphicsObject.__init__(self, parent)
         self.setAcceptedMouseButtons(QtCore.Qt.NoButton)
         pos = Point(pos)
         size = Point(size)
-        self.aspectLocked = False
+        self.aspectLocked = aspectLocked
         self.translatable = movable
         self.rotatable = rotatable
         self.resizable = resizable
@@ -678,7 +679,7 @@ class ROI(GraphicsObject):
         
         The format returned is a list of (name, pos) tuples.
         """
-        if index == None:
+        if index is None:
             positions = []
             for h in self.handles:
                 positions.append((h['name'], h['pos']))
@@ -691,7 +692,7 @@ class ROI(GraphicsObject):
         
         The format returned is a list of (name, pos) tuples.
         """
-        if index == None:
+        if index is None:
             positions = []
             for h in self.handles:
                 positions.append((h['name'], h['item'].scenePos()))
@@ -1298,7 +1299,7 @@ class ROI(GraphicsObject):
         """Return global transformation (rotation angle+translation) required to move 
         from relative state to current state. If relative state isn't specified,
         then we use the state of the ROI when mouse is pressed."""
-        if relativeTo == None:
+        if relativeTo is None:
             relativeTo = self.preMoveState
         st = self.getState()
         
@@ -1941,8 +1942,7 @@ class CircleROI(EllipseROI):
             if radius is None:
                 raise TypeError("Must provide either size or radius.")
             size = (radius*2, radius*2)
-        EllipseROI.__init__(self, pos, size, **args)
-        self.aspectLocked = True
+        EllipseROI.__init__(self, pos, size, aspectLocked=True, **args)
         
     def _addHandles(self):
         self.addScaleHandle([0.5*2.**-0.5 + 0.5, 0.5*2.**-0.5 + 0.5], [0.5, 0.5])
@@ -2307,16 +2307,15 @@ class CrosshairROI(ROI):
     """A crosshair ROI whose position is at the center of the crosshairs. By default, it is scalable, rotatable and translatable."""
     
     def __init__(self, pos=None, size=None, **kargs):
-        if size == None:
+        if size is None:
             size=[1,1]
-        if pos == None:
+        if pos is None:
             pos = [0,0]
         self._shape = None
-        ROI.__init__(self, pos, size, **kargs)
+        ROI.__init__(self, pos, size, aspectLocked=True, **kargs)
         
         self.sigRegionChanged.connect(self.invalidate)
         self.addScaleRotateHandle(Point(1, 0), Point(0, 0))
-        self.aspectLocked = True
 
     def invalidate(self):
         self._shape = None
@@ -2391,9 +2390,6 @@ class TriangleROI(ROI):
     """
 
     def __init__(self, pos, size, **args):
-        ROI.__init__(self, pos, [size, size], **args)
-        self.aspectLocked = True
-        angles = np.linspace(0, pi * 4 / 3, 3)
         ROI.__init__(self, pos, [size, size], aspectLocked=True, **args)
         angles = np.linspace(0, np.pi * 4 / 3, 3)
         verticies = (np.array((np.sin(angles), np.cos(angles))).T + 1.0) / 2.0
diff --git a/pyqtgraph/graphicsItems/TargetItem.py b/pyqtgraph/graphicsItems/TargetItem.py
index 40fcdfc0..1a4d5144 100644
--- a/pyqtgraph/graphicsItems/TargetItem.py
+++ b/pyqtgraph/graphicsItems/TargetItem.py
@@ -1,5 +1,4 @@
-from math import atan2, pi, degrees
-
+from math import atan2
 from ..Qt import QtGui, QtCore
 from ..Point import Point
 from .. import functions as fn
diff --git a/pyqtgraph/graphicsItems/ViewBox/ViewBox.py b/pyqtgraph/graphicsItems/ViewBox/ViewBox.py
index ac771c1c..8d60c577 100644
--- a/pyqtgraph/graphicsItems/ViewBox/ViewBox.py
+++ b/pyqtgraph/graphicsItems/ViewBox/ViewBox.py
@@ -550,7 +550,6 @@ class ViewBox(GraphicsWidget):
                     dy = 1
                 mn -= dy*0.5
                 mx += dy*0.5
-                xpad = 0.0
 
             # Make sure no nan/inf get through
             if not math.isfinite(mn) or not math.isfinite(mx):
diff --git a/pyqtgraph/imageview/ImageView.py b/pyqtgraph/imageview/ImageView.py
index 6f60170c..f934b36d 100644
--- a/pyqtgraph/imageview/ImageView.py
+++ b/pyqtgraph/imageview/ImageView.py
@@ -12,7 +12,7 @@ Widget used for displaying 2D or 3D data. Features:
   - ROI plotting
   - Image normalization through a variety of methods
 """
-import os, sys
+import os
 from math import log10
 import numpy as np
 
diff --git a/pyqtgraph/opengl/GLViewWidget.py b/pyqtgraph/opengl/GLViewWidget.py
index 0f380ec9..a309d7a0 100644
--- a/pyqtgraph/opengl/GLViewWidget.py
+++ b/pyqtgraph/opengl/GLViewWidget.py
@@ -5,7 +5,7 @@ import numpy as np
 from .. import Vector
 from .. import functions as fn
 import warnings
-from math import cos, sin, tan, degrees, radians
+from math import cos, sin, tan, radians
 ##Vector = QtGui.QVector3D
 
 ShareWidget = None
diff --git a/pyqtgraph/parametertree/SystemSolver.py b/pyqtgraph/parametertree/SystemSolver.py
index de177a37..d7b6bef8 100644
--- a/pyqtgraph/parametertree/SystemSolver.py
+++ b/pyqtgraph/parametertree/SystemSolver.py
@@ -398,9 +398,6 @@ if __name__ == '__main__':
                 # value at the same time.
                 sh = (1./60.)
                 raise
-            
-            
-            
             return ap
 
         def _balance(self):
@@ -408,8 +405,6 @@ if __name__ == '__main__':
             light = self.lightMeter
             sh = self.shutter
             ap = self.aperture
-            fl = self.flash
-            
             bal = (4.0 / ap) * (sh / (1./60.)) * (iso / 100.) * (2 ** light)
             return log2(bal)
     
diff --git a/pyqtgraph/widgets/GraphicsView.py b/pyqtgraph/widgets/GraphicsView.py
index 56304f51..d2b0f553 100644
--- a/pyqtgraph/widgets/GraphicsView.py
+++ b/pyqtgraph/widgets/GraphicsView.py
@@ -7,10 +7,7 @@ Distributed under MIT/X11 license. See license.txt for more information.
 
 from ..Qt import QtCore, QtGui, QtWidgets, QT_LIB
 from ..Point import Point
-import sys, os
-from .FileDialog import FileDialog
 from ..GraphicsScene import GraphicsScene
-import numpy as np
 from .. import functions as fn
 from .. import debug as debug
 from .. import getConfigOption