diff --git a/agents.ipynb b/agents.ipynb
index 7976b12b2..8eba9f07e 100644
--- a/agents.ipynb
+++ b/agents.ipynb
@@ -8,7 +8,7 @@
     "\n",
     "An agent, as defined in 2.1 is anything that can perceive its <b>environment</b> through sensors, and act upon that environment through actuators based on its <b>agent program</b>. This can be a dog, robot, or even you. As long as you can perceive the environment and act on it, you are an agent. This notebook will explain how to implement a simple agent, create an environment, and create a program that helps the agent act on the environment based on its percepts.\n",
     "\n",
-    "Before moving on, review the <b>Agent</b> and <b>Environment</b> classes in <b>[agents.py](https://github.com/aimacode/aima-python/blob/master/agents.py)</b>.\n",
+    "Before moving on, review the <b>Agent</b> and <b>Environment</b> classes in [<b>agents.py</b>](https://github.com/aimacode/aima-python/blob/master/agents.py).\n",
     "\n",
     "Let's begin by importing all the functions from the agents.py module and creating our first agent - a blind dog."
    ]
diff --git a/agents.py b/agents.py
index 650dfe97b..abd7b9f7a 100644
--- a/agents.py
+++ b/agents.py
@@ -55,16 +55,16 @@ def __repr__(self):
         return '<{}>'.format(getattr(self, '__name__', self.__class__.__name__))
 
     def is_alive(self):
-        "Things that are 'alive' should return true."
+        """Things that are 'alive' should return true."""
         return hasattr(self, 'alive') and self.alive
 
     def show_state(self):
-        "Display the agent's internal state.  Subclasses should override."
+        """Display the agent's internal state.  Subclasses should override."""
         print("I don't know how to show_state.")
 
     def display(self, canvas, x, y, width, height):
+        """Display an image of this Thing on the canvas."""
         # Do we need this?
-        "Display an image of this Thing on the canvas."
         pass
 
 
@@ -89,7 +89,7 @@ def __init__(self, program=None):
         self.performance = 0
         if program is None:
             def program(percept):
-                return eval(input('Percept={}; action? ' .format(percept)))
+                return eval(input('Percept={}; action? '.format(percept)))
         assert isinstance(program, collections.Callable)
         self.program = program
 
@@ -129,14 +129,14 @@ def program(percept):
 
 
 def RandomAgentProgram(actions):
-    "An agent that chooses an action at random, ignoring all percepts."
+    """An agent that chooses an action at random, ignoring all percepts."""
     return lambda percept: random.choice(actions)
 
 # ______________________________________________________________________________
 
 
 def SimpleReflexAgentProgram(rules, interpret_input):
-    "This agent takes action based solely on the percept. [Figure 2.10]"
+    """This agent takes action based solely on the percept. [Figure 2.10]"""
     def program(percept):
         state = interpret_input(percept)
         rule = rule_match(state, rules)
@@ -146,7 +146,7 @@ def program(percept):
 
 
 def ModelBasedReflexAgentProgram(rules, update_state, model):
-    "This agent takes action based on the percept and state. [Figure 2.8]"
+    """This agent takes action based on the percept and state. [Figure 2.8]"""
     def program(percept):
         program.state = update_state(program.state, program.action, percept, model)
         rule = rule_match(program.state, rules)
@@ -157,7 +157,7 @@ def program(percept):
 
 
 def rule_match(state, rules):
-    "Find the first rule that matches state."
+    """Find the first rule that matches state."""
     for rule in rules:
         if rule.matches(state):
             return rule
@@ -168,12 +168,12 @@ def rule_match(state, rules):
 
 
 def RandomVacuumAgent():
-    "Randomly choose one of the actions from the vacuum environment."
+    """Randomly choose one of the actions from the vacuum environment."""
     return Agent(RandomAgentProgram(['Right', 'Left', 'Suck', 'NoOp']))
 
 
 def TableDrivenVacuumAgent():
-    "[Figure 2.3]"
+    """[Figure 2.3]"""
     table = {((loc_A, 'Clean'),): 'Right',
              ((loc_A, 'Dirty'),): 'Suck',
              ((loc_B, 'Clean'),): 'Left',
@@ -189,7 +189,7 @@ def TableDrivenVacuumAgent():
 
 
 def ReflexVacuumAgent():
-    "A reflex agent for the two-state vacuum environment. [Figure 2.8]"
+    """A reflex agent for the two-state vacuum environment. [Figure 2.8]"""
     def program(percept):
         location, status = percept
         if status == 'Dirty':
@@ -202,11 +202,11 @@ def program(percept):
 
 
 def ModelBasedVacuumAgent():
-    "An agent that keeps track of what locations are clean or dirty."
+    """An agent that keeps track of what locations are clean or dirty."""
     model = {loc_A: None, loc_B: None}
 
     def program(percept):
-        "Same as ReflexVacuumAgent, except if everything is clean, do NoOp."
+        """Same as ReflexVacuumAgent, except if everything is clean, do NoOp."""
         location, status = percept
         model[location] = status  # Update the model here
         if model[loc_A] == model[loc_B] == 'Clean':
@@ -242,32 +242,29 @@ def thing_classes(self):
         return []  # List of classes that can go into environment
 
     def percept(self, agent):
-        '''
-            Return the percept that the agent sees at this point.
-            (Implement this.)
-        '''
+        """Return the percept that the agent sees at this point. (Implement this.)"""
         raise NotImplementedError
 
     def execute_action(self, agent, action):
-        "Change the world to reflect this action. (Implement this.)"
+        """Change the world to reflect this action. (Implement this.)"""
         raise NotImplementedError
 
     def default_location(self, thing):
-        "Default location to place a new thing with unspecified location."
+        """Default location to place a new thing with unspecified location."""
         return None
 
     def exogenous_change(self):
-        "If there is spontaneous change in the world, override this."
+        """If there is spontaneous change in the world, override this."""
         pass
 
     def is_done(self):
-        "By default, we're done when we can't find a live agent."
+        """By default, we're done when we can't find a live agent."""
         return not any(agent.is_alive() for agent in self.agents)
 
     def step(self):
         """Run the environment for one time step. If the
         actions and exogenous changes are independent, this method will
-        do.  If there are interactions between them, you'll need to
+        do. If there are interactions between them, you'll need to
         override this method."""
         if not self.is_done():
             actions = []
@@ -281,14 +278,14 @@ def step(self):
             self.exogenous_change()
 
     def run(self, steps=1000):
-        "Run the Environment for given number of time steps."
+        """Run the Environment for given number of time steps."""
         for step in range(steps):
             if self.is_done():
                 return
             self.step()
 
     def list_things_at(self, location, tclass=Thing):
-        "Return all things exactly at a given location."
+        """Return all things exactly at a given location."""
         return [thing for thing in self.things
                 if thing.location == location and isinstance(thing, tclass)]
 
@@ -317,19 +314,19 @@ def delete_thing(self, thing):
         except ValueError as e:
             print(e)
             print("  in Environment delete_thing")
-            print("  Thing to be removed: {} at {}" .format(thing, thing.location))
-            print("  from list: {}" .format([(thing, thing.location) for thing in self.things]))
+            print("  Thing to be removed: {} at {}".format(thing, thing.location))
+            print("  from list: {}".format([(thing, thing.location) for thing in self.things]))
         if thing in self.agents:
             self.agents.remove(thing)
 
 class Direction():
-    '''A direction class for agents that want to move in a 2D plane
+    """A direction class for agents that want to move in a 2D plane
         Usage:
             d = Direction("down")
             To change directions:
             d = d + "right" or d = d + Direction.R #Both do the same thing
             Note that the argument to __add__ must be a string and not a Direction object.
-            Also, it (the argument) can only be right or left.'''
+            Also, it (the argument) can only be right or left."""
 
     R = "right"
     L = "left"
@@ -396,7 +393,7 @@ def __init__(self, width=10, height=10):
     perceptible_distance = 1
 
     def things_near(self, location, radius=None):
-        "Return all things within radius of location."
+        """Return all things within radius of location."""
         if radius is None:
             radius = self.perceptible_distance
         radius2 = radius * radius
@@ -404,7 +401,7 @@ def things_near(self, location, radius=None):
                 if distance2(location, thing.location) <= radius2]
 
     def percept(self, agent):
-        '''By default, agent perceives things within a default radius.'''
+        """By default, agent perceives things within a default radius."""
         return self.things_near(agent.location)
 
     def execute_action(self, agent, action):
@@ -428,8 +425,8 @@ def default_location(self, thing):
         return (random.choice(self.width), random.choice(self.height))
 
     def move_to(self, thing, destination):
-        '''Move a thing to a new location. Returns True on success or False if there is an Obstacle.
-            If thing is holding anything, they move with him.'''
+        """Move a thing to a new location. Returns True on success or False if there is an Obstacle.
+        If thing is holding anything, they move with him."""
         thing.bump = self.some_things_at(destination, Obstacle)
         if not thing.bump:
             thing.location = destination
@@ -449,9 +446,8 @@ def move_to(self, thing, destination):
     #         obs.thing_added(thing)
 
     def add_thing(self, thing, location=(1, 1), exclude_duplicate_class_items=False):
-        '''Adds things to the world.
-            If (exclude_duplicate_class_items) then the item won't be added if the location
-            has at least one item of the same class.'''
+        """Adds things to the world. If (exclude_duplicate_class_items) then the item won't be 
+        added if the location has at least one item of the same class."""
         if (self.is_inbounds(location)):
             if (exclude_duplicate_class_items and
                 any(isinstance(t, thing.__class__) for t in self.list_things_at(location))):
@@ -459,12 +455,12 @@ def add_thing(self, thing, location=(1, 1), exclude_duplicate_class_items=False)
             super(XYEnvironment, self).add_thing(thing, location)
 
     def is_inbounds(self, location):
-        '''Checks to make sure that the location is inbounds (within walls if we have walls)'''
+        """Checks to make sure that the location is inbounds (within walls if we have walls)"""
         x,y = location
         return not (x < self.x_start or x >= self.x_end or y < self.y_start or y >= self.y_end)
 
     def random_location_inbounds(self, exclude=None):
-        '''Returns a random location that is inbounds (within walls if we have walls)'''
+        """Returns a random location that is inbounds (within walls if we have walls)"""
         location = (random.randint(self.x_start, self.x_end), random.randint(self.y_start, self.y_end))
         if exclude is not None:
             while(location == exclude):
@@ -472,7 +468,7 @@ def random_location_inbounds(self, exclude=None):
         return location
 
     def delete_thing(self, thing):
-        '''Deletes thing, and everything it is holding (if thing is an agent)'''
+        """Deletes thing, and everything it is holding (if thing is an agent)"""
         if isinstance(thing, Agent):
             for obj in thing.holding:
                 super(XYEnvironment, self).delete_thing(obj)
@@ -484,7 +480,7 @@ def delete_thing(self, thing):
             obs.thing_deleted(thing)
 
     def add_walls(self):
-        '''Put walls around the entire perimeter of the grid.'''
+        """Put walls around the entire perimeter of the grid."""
         for x in range(self.width):
             self.add_thing(Wall(), (x, 0))
             self.add_thing(Wall(), (x, self.height - 1))
@@ -506,7 +502,7 @@ def add_observer(self, observer):
         self.observers.append(observer)
 
     def turn_heading(self, heading, inc):
-        "Return the heading to the left (inc=+1) or right (inc=-1) of heading."
+        """Return the heading to the left (inc=+1) or right (inc=-1) of heading."""
         return turn_heading(heading, inc)
 
 
@@ -526,7 +522,8 @@ class Wall(Obstacle):
 # Continuous environment
 
 class ContinuousWorld(Environment):
-    """ Model for Continuous World."""
+    """Model for Continuous World."""
+
     def __init__(self, width=10, height=10):
         super(ContinuousWorld, self).__init__()
         self.width = width
@@ -537,8 +534,9 @@ def add_obstacle(self, coordinates):
 
 
 class PolygonObstacle(Obstacle):
+
     def __init__(self, coordinates):
-        """ Coordinates is a list of tuples."""
+        """Coordinates is a list of tuples."""
         super(PolygonObstacle, self).__init__()
         self.coordinates = coordinates
 
@@ -604,7 +602,7 @@ def thing_classes(self):
                 TableDrivenVacuumAgent, ModelBasedVacuumAgent]
 
     def percept(self, agent):
-        "Returns the agent's location, and the location status (Dirty/Clean)."
+        """Returns the agent's location, and the location status (Dirty/Clean)."""
         return (agent.location, self.status[agent.location])
 
     def execute_action(self, agent, action):
@@ -622,7 +620,7 @@ def execute_action(self, agent, action):
             self.status[agent.location] = 'Clean'
 
     def default_location(self, thing):
-        "Agents start in either location at random."
+        """Agents start in either location at random."""
         return random.choice([loc_A, loc_B])
 
 # ______________________________________________________________________________
@@ -632,7 +630,7 @@ def default_location(self, thing):
 class Gold(Thing):
 
     def __eq__(self, rhs):
-        '''All Gold are equal'''
+        """All Gold are equal"""
         return rhs.__class__ == Gold
     pass
 
@@ -648,7 +646,6 @@ class Pit(Thing):
 class Breeze(Thing):
     pass
 
-
 class Arrow(Thing):
     pass
 
@@ -671,7 +668,7 @@ class Explorer(Agent):
     direction = Direction("right")
 
     def can_grab(self, thing):
-        '''Explorer can only grab gold'''
+        """Explorer can only grab gold"""
         return thing.__class__ == Gold
 
 
@@ -684,7 +681,7 @@ def __init__(self, agent_program, width=6, height=6):
         self.init_world(agent_program)
 
     def init_world(self, program):
-        '''Spawn items to the world based on probabilities from the book'''
+        """Spawn items to the world based on probabilities from the book"""
 
         "WALLS"
         self.add_walls()
@@ -715,7 +712,7 @@ def init_world(self, program):
         self.add_thing(Explorer(program), (1, 1), True)
 
     def get_world(self, show_walls=True):
-        '''Returns the items in the world'''
+        """Returns the items in the world"""
         result = []
         x_start, y_start = (0, 0) if show_walls else (1, 1)
         x_end, y_end = (self.width, self.height) if show_walls else (self.width - 1, self.height - 1)
@@ -727,16 +724,16 @@ def get_world(self, show_walls=True):
         return result
 
     def percepts_from(self, agent, location, tclass=Thing):
-        '''Returns percepts from a given location, and replaces some items with percepts from chapter 7.'''
+        """Returns percepts from a given location, and replaces some items with percepts from chapter 7."""
         thing_percepts = {
             Gold: Glitter(),
             Wall: Bump(),
             Wumpus: Stench(),
             Pit: Breeze()}
-        '''Agents don't need to get their percepts'''
+        """Agents don't need to get their percepts"""
         thing_percepts[agent.__class__] = None
 
-        '''Gold only glitters in its cell'''
+        """Gold only glitters in its cell"""
         if location != agent.location:
             thing_percepts[Gold] = None
 
@@ -746,8 +743,8 @@ def percepts_from(self, agent, location, tclass=Thing):
         return result if len(result) else [None]
 
     def percept(self, agent):
-        '''Returns things in adjacent (not diagonal) cells of the agent.
-            Result format: [Left, Right, Up, Down, Center / Current location]'''
+        """Returns things in adjacent (not diagonal) cells of the agent.
+        Result format: [Left, Right, Up, Down, Center / Current location]"""
         x, y = agent.location
         result = []
         result.append(self.percepts_from(agent, (x - 1, y)))
@@ -756,7 +753,7 @@ def percept(self, agent):
         result.append(self.percepts_from(agent, (x, y + 1)))
         result.append(self.percepts_from(agent, (x, y)))
 
-        '''The wumpus gives out a a loud scream once it's killed.'''
+        """The wumpus gives out a a loud scream once it's killed."""
         wumpus = [thing for thing in self.things if isinstance(thing, Wumpus)]
         if len(wumpus) and not wumpus[0].alive and not wumpus[0].screamed:
             result[-1].append(Scream())
@@ -765,8 +762,8 @@ def percept(self, agent):
         return result
 
     def execute_action(self, agent, action):
-        '''Modify the state of the environment based on the agent's actions.
-            Performance score taken directly out of the book.'''
+        """Modify the state of the environment based on the agent's actions.
+        Performance score taken directly out of the book."""
 
         if isinstance(agent, Explorer) and self.in_danger(agent):
             return
@@ -794,7 +791,7 @@ def execute_action(self, agent, action):
                 agent.performance += 1000 if Gold() in agent.holding else 0
                 self.delete_thing(agent)
         elif action == 'Shoot':
-            '''The arrow travels straight down the path the agent is facing'''
+            """The arrow travels straight down the path the agent is facing"""
             if agent.has_arrow:
                 arrow_travel = agent.direction.move_forward(agent.location)
                 while(self.is_inbounds(arrow_travel)):
@@ -807,7 +804,7 @@ def execute_action(self, agent, action):
                 agent.has_arrow = False
 
     def in_danger(self, agent):
-        '''Checks if Explorer is in danger (Pit or Wumpus), if he is, kill him'''
+        """Checks if Explorer is in danger (Pit or Wumpus), if he is, kill him"""
         for thing in self.list_things_at(agent.location):
             if isinstance(thing, Pit) or (isinstance(thing, Wumpus) and thing.alive):
                 agent.alive = False
@@ -817,8 +814,8 @@ def in_danger(self, agent):
         return False
 
     def is_done(self):
-        '''The game is over when the Explorer is killed
-            or if he climbs out of the cave only at (1,1).'''
+        """The game is over when the Explorer is killed
+        or if he climbs out of the cave only at (1,1)."""
         explorer = [agent for agent in self.agents if isinstance(agent, Explorer) ]
         if len(explorer):
                 if explorer[0].alive:
@@ -845,7 +842,7 @@ def compare_agents(EnvFactory, AgentFactories, n=10, steps=1000):
 
 
 def test_agent(AgentFactory, steps, envs):
-    "Return the mean score of running an agent in each of the envs, for steps"
+    """Return the mean score of running an agent in each of the envs, for steps"""
     def score(env):
         agent = AgentFactory()
         env.add_thing(agent)