diff --git a/ch-8/3-avoid/avoid_walls.py b/ch-8/3-avoid/avoid_walls.py
index 7e0a540..2d031af 100644
--- a/ch-8/3-avoid/avoid_walls.py
+++ b/ch-8/3-avoid/avoid_walls.py
@@ -11,33 +11,41 @@ robot.left_distance.start_ranging()
 robot.right_distance.start_ranging()
 
 try:
-  robot.set_left(speed)
-  robot.set_right(speed)
-  
-  while True:
-    # do we have data:
-    if robot.left_distance.data_ready and robot.right_distance.data_ready:
-      left_dist = robot.left_distance.distance
-      right_dist = robot.right_distance.distance
-      # are any too close
-      if right_dist < too_close_cm:
-        print("Obstacle detected - Left: {} cm, Right: {} cm".format(left_dist, right_dist))
-        robot.set_left(-speed)
-      else:
-        robot.set_left(speed)
-        if left_dist < too_close_cm:
-          print("Obstacle detected - Left: {} cm, Right: {} cm".format(left_dist, right_dist))
-          robot.set_right(-speed)
-        else:
-          robot.set_right(speed)
+    robot.set_left(speed)
+    robot.set_right(speed)
 
-      robot.left_distance.clear_interrupt()
-      robot.right_distance.clear_interrupt()
-      time.sleep(0.1)
+    while True:
+        # do we have data:
+        if robot.left_distance.data_ready and robot.right_distance.data_ready:
+            left_dist = robot.left_distance.distance
+            right_dist = robot.right_distance.distance
+            # are any too close
+            if right_dist < too_close_cm:
+                print(
+                    "Obstacle detected - Left: {} cm, Right: {} cm".format(
+                        left_dist, right_dist
+                    )
+                )
+                robot.set_left(-speed)
+            else:
+                robot.set_left(speed)
+                if left_dist < too_close_cm:
+                    print(
+                        "Obstacle detected - Left: {} cm, Right: {} cm".format(
+                            left_dist, right_dist
+                        )
+                    )
+                    robot.set_right(-speed)
+                else:
+                    robot.set_right(speed)
+
+            robot.left_distance.clear_interrupt()
+            robot.right_distance.clear_interrupt()
+            time.sleep(0.1)
 
 finally:
-  robot.stop()
-  robot.left_distance.clear_interrupt()
-  robot.right_distance.clear_interrupt()
-  robot.left_distance.stop_ranging()
-  robot.right_distance.stop_ranging()
+    robot.stop()
+    robot.left_distance.clear_interrupt()
+    robot.right_distance.clear_interrupt()
+    robot.left_distance.stop_ranging()
+    robot.right_distance.stop_ranging()
diff --git a/ch-8/3-avoid/pio_encoder.py b/ch-8/3-avoid/pio_encoder.py
index e9202f8..ffcc9f2 100644
--- a/ch-8/3-avoid/pio_encoder.py
+++ b/ch-8/3-avoid/pio_encoder.py
@@ -54,24 +54,24 @@ send:
 
 assembled = adafruit_pioasm.assemble(program)
 
-class QuadratureEncoder:
-  def __init__(self, first_pin, second_pin, reversed=False):
-    """Encoder with 2 pins. Must use sequential pins on the board"""
-    self.sm = rp2pio.StateMachine(
-        assembled,
-        frequency=0,
-        first_in_pin=first_pin,
-        jmp_pin=second_pin,
-        in_pin_count=2
-    )
-    self.reversed = reversed
-    self._buffer = array.array('i', [0])
 
-  def read(self):
-    while self.sm.in_waiting:
-      self.sm.readinto(self._buffer)
-    if self.reversed:
-      return -self._buffer[0]
-    else:
-      return self._buffer[0]
- 
\ No newline at end of file
+class QuadratureEncoder:
+    def __init__(self, first_pin, second_pin, reversed=False):
+        """Encoder with 2 pins. Must use sequential pins on the board"""
+        self.sm = rp2pio.StateMachine(
+            assembled,
+            frequency=0,
+            first_in_pin=first_pin,
+            jmp_pin=second_pin,
+            in_pin_count=2,
+        )
+        self.reversed = reversed
+        self._buffer = array.array("i", [0])
+
+    def read(self):
+        while self.sm.in_waiting:
+            self.sm.readinto(self._buffer)
+        if self.reversed:
+            return -self._buffer[0]
+        else:
+            return self._buffer[0]
diff --git a/ch-8/3-avoid/robot.py b/ch-8/3-avoid/robot.py
index 1b339ef..a564a9b 100755
--- a/ch-8/3-avoid/robot.py
+++ b/ch-8/3-avoid/robot.py
@@ -29,6 +29,7 @@ def stop():
     motor_B1.duty_cycle = 0
     motor_B2.duty_cycle = 0
 
+
 def set_speed(motor, speed):
     # Swap motor pins if we reverse the speed
     if speed < 0:
@@ -36,15 +37,16 @@ def set_speed(motor, speed):
         speed = -speed
     else:
         direction = motor
-    speed = min(speed, 1) # limit to 1.0
-    max_speed = 2**16-1
-
+    speed = min(speed, 1)  # limit to 1.0
+    max_speed = 2 ** 16 - 1
 
     direction[0].duty_cycle = int(max_speed * speed)
     direction[1].duty_cycle = 0
 
+
 def set_left(speed):
     set_speed(left_motor, speed)
 
+
 def set_right(speed):
     set_speed(right_motor, speed)
diff --git a/ch-8/3-avoid/varying_wall_avoid.py b/ch-8/3-avoid/varying_wall_avoid.py
index 16ff455..532c278 100644
--- a/ch-8/3-avoid/varying_wall_avoid.py
+++ b/ch-8/3-avoid/varying_wall_avoid.py
@@ -1,4 +1,3 @@
-
 import robot
 import time
 
@@ -9,32 +8,38 @@ robot.right_distance.start_ranging()
 
 speed = 0.9
 
+
 def speed_from_distance(distance):
-  limited_distance = min(distance, 30) * speed
-  return limited_distance / 30
+    limited_distance = min(distance, 30) * speed
+    return limited_distance / 30
+
 
 try:
-  robot.set_left(speed)
-  robot.set_right(speed)
-  
-  while True:
-    # do we have data:
-    if robot.left_distance.data_ready and robot.right_distance.data_ready:
-      left_dist = robot.left_distance.distance
-      right_dist = robot.right_distance.distance
-      l_speed = speed_from_distance(robot.right_distance.distance)
-      r_speed = speed_from_distance(robot.left_distance.distance)
-      print("Left: {} cm R Sp: {}, Right: {} cm L Sp: {}".format(left_dist, r_speed, right_dist, l_speed))
-      robot.set_left(l_speed)
-      robot.set_right(r_speed)
+    robot.set_left(speed)
+    robot.set_right(speed)
 
-      robot.left_distance.clear_interrupt()
-      robot.right_distance.clear_interrupt()
-      time.sleep(0.1)
+    while True:
+        # do we have data:
+        if robot.left_distance.data_ready and robot.right_distance.data_ready:
+            left_dist = robot.left_distance.distance
+            right_dist = robot.right_distance.distance
+            l_speed = speed_from_distance(robot.right_distance.distance)
+            r_speed = speed_from_distance(robot.left_distance.distance)
+            print(
+                "Left: {} cm R Sp: {}, Right: {} cm L Sp: {}".format(
+                    left_dist, r_speed, right_dist, l_speed
+                )
+            )
+            robot.set_left(l_speed)
+            robot.set_right(r_speed)
+
+            robot.left_distance.clear_interrupt()
+            robot.right_distance.clear_interrupt()
+            time.sleep(0.1)
 
 finally:
-  robot.stop()
-  robot.left_distance.clear_interrupt()
-  robot.right_distance.clear_interrupt()
-  robot.left_distance.stop_ranging()
-  robot.right_distance.stop_ranging()
+    robot.stop()
+    robot.left_distance.clear_interrupt()
+    robot.right_distance.clear_interrupt()
+    robot.left_distance.stop_ranging()
+    robot.right_distance.stop_ranging()