Tony Ballantyne Tech

We now have a working game, however the code isn’t very robust. Robust code continues to function when errors occur.

Here’s an example of the start of a game:

A clearing in a forest
spanner
lockpick
What now?use spade
What now?use spoon
Traceback (most recent call last):
  File "M:/PycharmProjects/Adventure/ad6.py", line 81, in <module>
    Main()
  File "M:/PycharmProjects/Adventure/ad6.py", line 75, in Main
    if (objects[noun]==99): # check holding object
KeyError: 'spoon'

Process finished with exit code 1

There are two problems here, one minor, one major.

The minor problem occurs when the user types use spade. Nothing happens as the user isn’t holding a spade, but the program doesn’t alert the user to that fact.

The major problem occurs when the user tries to use spoon. At that point the program throws an exception and terminates.

An exception is an error that occurs when the program is running and causes the program to terminate. In this case, the program is trying to look up an object that doesn’t exist. We need to handle this exception.

The following code deals with both the above problems.

elif verb == "use":
            try:
                if (objects[noun]==99): # check holding object
                    use_object(noun)
                else:
                    print("I don't have a", noun)
            except:
                print("I don't know what a", noun, "is")

You will see try except in many pieces of python code. It’s the professional way to write robust code

Here’s the complete code. Copy and paste it into your IDE

places = ["A clearing in a forest", "An old wooden cabin", "A dark cave", "The top of a Hill", "Deep in the Forest", "An Underground Lake", "Caught in the Brambles"]
moves = [{"n": 1, "s": 2, "e":4},     {"s": 0, "e":3},       {"n": 0} ,     {"w": 1, "s":4},    {"n":3,"w":1, "e":6}, {"w": 2},             {"w": 4}]
objects = {"spanner":0,  "lockpick":0, "spade":2}
location = 0

def print_objects():
    for key, val in objects.items():
        if val == location:
            print(key)

def items():
    print("You are carrying: ")
    for key, val in objects.items():
        if val == 99:
            print(key)


def take_object(noun):
    for key, val in objects.items():
        if key == noun and val == location:
            print("Got it!")
            objects[noun] = 99

def drop_object(noun):
    for key, val in objects.items():
        if key ==noun and val == 99:
            print("Dropped ", noun)
            objects[noun] = location

def use_object(noun):
    if noun == "spade" and location == 0:
        objects["gold"] = 0 # create the gold
        print("You dug up some gold!")
    if noun == "spade" and location == 2:
        moves[2] = {"n": 0, "e":5}
        print("You've opened up a tunnel, leading east...")


def Main():
    ans = ""
    global location
    print(places[0])
    print_objects()


    while ans != "bye":
        ans = input("What now?")
        words = ans.split()

        # Check if it's a move
        if len(words) == 1:
            if ans == "items":
                items()
            elif ans == "look":
                print(places[location])
                print_objects()

            elif ans in moves[location]:
                location = moves[location].get(ans)
                print(places[location])
                print_objects()
            else:
                print("I can't move that way")
        else:
            verb = words[0] # e.g. Take or Drop
            noun = words[1] # e.g. hammer or spanner

            if verb == "take":
                take_object(noun)

            elif verb == "drop":
                drop_object(noun)

            elif verb == "use":
                try:
                    if (objects[noun]==99): # check holding object
                        use_object(noun)
                    else:
                        print("I don't have a", noun)
                except:
                    print("I don't know what a", noun, "is")

            else:
                print("I don't understand what you mean")

Main()

Exercise

1. Copy the above code into your IDE and test it.
2. Run the code. What happens if you try to take the spade in the clearing in the forest?
3. Is the behaviour of the code here an error or an exception?
4. Fix the code.
5. What errors can occur when a user tries to drop an object? Fix those errors.
6. What other errors can you find in the code?
7. Are there any other exceptions you can find in the code?

• Adventure Game 1
• Adventure Game 2: Add Objects
• Adventure Game 3: Take and Drop Objects
• Adventure Game 4: Structured Programming
• Adventure Game 5: Adding New Commands and Tidying Old Ones
• Adventure Game 6: Using Objects
• => Adventure Game 7: Robust Code
• Adventure Game 8: Making a Playable Game

We’ve set up the basics of the game, but it’s not much fun. All you can do is wander round picking up and dropping objects. We need to allow the user to use the objects. We’re going to add two ways of using objects.

• If the player uses the spade in the clearing in the forest they will dig up gold.
• If the player uses the spade in the cave they will open a path to an underground lake.

Note that I’ve added new locations to the map, the same ones we added in Exercise 1

places = ["A clearing in a forest", "An old wooden cabin", "A dark cave", "The top of a Hill", "Deep in the Forest", "An Underground Lake", "Caught in the Brambles"]
moves = [{"n": 1, "s": 2, "e":4},     {"s": 0, "e":3},       {"n": 0} ,     {"w": 1, "s":4},    {"n":3,"w":1, "e":6}, {"w": 2},             {"w": 4}]
objects = {"spanner":0,  "lockpick":0, "spade":2}
location = 0

def print_objects():
    for key, val in objects.items():
        if val == location:
            print(key)

def items():
    print("You are carrying: ")
    for key, val in objects.items():
        if val == 99:
            print(key)


def take_object(noun):
    for key, val in objects.items():
        if key == noun and val == location:
            print("Got it!")
            objects[noun] = 99

def drop_object(noun):
    for key, val in objects.items():
        if key ==noun and val == 99:
            print("Dropped ", noun)
            objects[noun] = location

def use_object(noun):
    if noun == "spade" and location == 0:
        objects["gold"] = 0 # create the gold
        print("You dug up some gold!")
    if noun == "spade" and location == 2:
        moves[2] = {"n": 0, "e":5}
        print("You've opened up a tunnel, leading east...")


def Main():
    ans = ""
    global location
    print(places[0])
    print_objects()


    while ans != "bye":
        ans = input("What now?")
        words = ans.split()

        # Check if it's a move
        if len(words) == 1:
            if ans == "items":
                items()
            elif ans == "look":
                print(places[location])
                print_objects()

            elif ans in moves[location]:
                location = moves[location].get(ans)
                print(places[location])
                print_objects()
            else:
                print("I can't move that way")
        else:
            verb = words[0] # e.g. Take or Drop
            noun = words[1] # e.g. hammer or spanner

            if verb == "take":
                take_object(noun)

            elif verb == "drop":
                drop_object(noun)

            elif verb == "use":
                if (objects[noun]==99): # check holding object
                    use_object(noun)

            else:
                print("I don't understand what you mean")

Main()

Exercise

1. Copy the code into your IDE. Move around the map to see the new locations
2. Find the spade and use it to dig up gold in the forest
3. Now dig in the cave and check to see the path to the lake opens up.
4. Look at the function use_object(noun). What’s the purpose of the statement objects["gold"] = 0
5. Look at the moves list (line 2). What has been added to the first dictionary in the list?
6. Look at moves[2] (remember, this is the third item in the list). At the moment this is {“n”: 0}. What does that mean?
7. Look at the function use_object(noun). What is the purpose of the line moves[2] = {"n": 0, "e":5} (hint, this is only called if the noun is a spade)
8. Add the following objects to the map: telescope in the wooden cabin, cutters deep in the forest.
9. Add code so if the user uses the telescope on top of the hill they see a message written on a sign saying “There is treasure in the forest”
10. Add code so if the user uses the cutters when caught in the brambles, treasure appears.

• Adventure Game 1
• Adventure Game 2: Add Objects
• Adventure Game 3: Take and Drop Objects
• Adventure Game 4: Structured Programming
• Adventure Game 5: Adding New Commands and Tidying Old Ones
• => Adventure Game 6: Using Objects
• Adventure Game 7: Robust Code
• Adventure Game 8: Making a Playable Game

We’re going to add two new commands, Look and Items

• Look will show your current location and objects
• Items will show the items you’re currently carrying

places = ["A clearing in a forest", "An old wooden cabin", "A dark cave"]
moves = [{"n": 1, "s": 2},           {"s": 0},              {"n": 0}]
objects = {"spanner":0,  "lockpick":0, "spade":2}
location = 0

def print_objects():
    for key, val in objects.items():
        if val == location:
            print(key)

def items():
    print("You are carrying: ")
    for key, val in objects.items():
        if val == 99:
            print(key)


def take_object(noun):
    for key, val in objects.items():
        if key == noun and val == location:
            print("Got it!")
            objects[noun] = 99

def drop_object(noun):
    for key, val in objects.items():
        if key ==noun and val == 99:
            print("Dropped ", noun)
            objects[noun] = location


def Main():
    ans = ""
    global location
    print(places[0])
    print_objects()


    while ans != "bye":
        ans = input("What now?")
        words = ans.split()

        # Check if it's a one word input
        if len(words) == 1:
            if ans == "items":
                items()
            elif ans == "look":
                print(places[location])
                print_objects()
            elif ans in moves[location]:
                location = moves[location].get(ans)
                print(places[location])
                print_objects()
            else:
                print("I can't move that way")
        else:
            verb = words[0] # e.g. Take or Drop
            noun = words[1] # e.g. hammer or spanner

            if verb == "take":
                take_object(noun)

            elif verb == "drop":
                drop_object(noun)

            else:
                print("I don't understand what you mean")

Main()

Exercise

1. Look at the Main() function. Why is location a global variable?
2. List the one word commands that are permitted in this program
3. What does the print_objects() function do?
4. Look at the items() function. Why does it only print items where val =99?

You’re going to add a help function. If the user enters “help” the program will print the following instructions: “Type n,s,e,w to move north, south, east and west.”

1. Add an elif statment under the elif ans == “look”: statement to check if the user has entered “help”
2. Add code to print the help instructions

• Adventure Game 1
• Adventure Game 2: Add Objects
• Adventure Game 3: Take and Drop Objects
• Adventure Game 4: Structured Programming
• => Adventure Game 5: Adding New Commands and Tidying Old Ones
• Adventure Game 6: Using Objects
• Adventure Game 7: Robust Code
• Adventure Game 8: Making a Playable Game

The program is becoming very complicated. We need to apply structured programming techniques to make it easier to follow. According to the specification this means:

“Using modularised programming, clear, well documented interfaces (local variables, parameters) and return values.”

Copy the following code into your IDE

places = ["A clearing in a forest", "An old wooden cabin", "A dark cave"]
moves = [{"n": 1, "s": 2},           {"s": 0},              {"n": 0}]
objects = {"spanner":0,  "lockpick":0, "spade":2}
location = 0

def print_objects():
    for key, val in objects.items():
        if val == location:
            print(key)

def take_object(noun):
    for key, val in objects.items():
        if key == noun and val == location:
            print("Got it!")
            objects[noun] = 99

def drop_object(noun):
    for key, val in objects.items():
        if key ==noun and val == 99:
            print("Dropped ", noun)
            objects[noun] = location


def Main():
    ans = ""
    global location
    print(places[0])
    print_objects()


    while ans != "bye":
        ans = input("What now?")
        words = ans.split()

        # Check if it's a move
        if len(words) == 1:            
            if ans in moves[location]:
                location = moves[location].get(ans)
                print(places[location])
                print_objects()
            else:
                print("I can't move that way")
        else:
            verb = words[0] # e.g. Take or Drop
            noun = words[1] # e.g. hammer or spanner

            if verb == "take":
                take_object(noun)

            elif verb == "drop":
                drop_object(noun)

            else:
                print("I don't understand what you mean")

Main()

Exercise

1. Copy the code into an IDE and run it. Check that it works
2. Give an example of a local variable in the code.
3. Give an example of a global variable.
4. Give an example of a parameter.
5. How many functions have parameters passed to them?
6. What are the advantages of the modular approach?
7. Add a function eat_object(noun). The function will print “I can’t eat” + noun.
8. Add code to the Main method to call the eat_object() function

• Adventure Game 1
• Adventure Game 2: Add Objects
• Adventure Game 3: Take and Drop Objects
• => Adventure Game 4: Structured Programming
• Adventure Game 5: Adding New Commands and Tidying Old Ones
• Adventure Game 6: Using Objects
• Adventure Game 7: Robust Code
• Adventure Game 8: Making a Playable Game

We added objects to the game in the last lesson. Now we’re going to add code to allow the user to take and drop objects

Copy and paste the following code into your IDE

places = ["A clearing in a forest", "An old wooden cabin", "A dark cave"]
moves = [{"n": 1, "s": 2},           {"s": 0},              {"n": 0}]
objects = {"spanner":0,  "lockpick":0, "spade":2}
location = 0

def print_objects():
    for key, val in objects.items():
        if val == location:
            print(key)

def Main():
    ans = ""
    global location
    print(places[0])
    print_objects()


    while ans != "bye":
        ans = input("What now?")
        words = ans.split()

        # Check if it's a move
        if len(words) == 1:
            if ans in moves[location]:
                location = moves[location].get(ans)
                print(places[location])
                print_objects()
            else:
                print("I can't move that way")
        else:
            verb = words[0] # e.g. Take or Drop
            noun = words[1] # e.g. hammer or spanner
            if verb == "take":
                for key, val in objects.items():
                    if key == noun and val == location:
                        print("Got it!")
                        objects[noun] = 99
            if verb == "drop":
                for key, val in objects.items():
                    if key ==noun and val == 99:
                        print("Dropped ", noun)
                        objects[noun] = location


Main()

Exercise

1. Run the game. Take the spanner and drop it in the cave. Check that everything is working correctly.
2. Add a spoon to the list of objects. Place the spoon in the cave. Check that you can Take it and Drop it.
3. What happens if you enter “take elephant?”
4. Look at the line words = ans.split() in the Main() function. What does it do? (try experimenting with the code in IDLE if you’re unsure)
5. Look at the if statement in the Main() function: if len(words) == 1: Why was that code included?
6. Look at the statement if verb == "take": What do key and val mean in the for loop?
7. What is the purpose of the for loop?
8. What is the purpose of the line 'objects[noun] == 99'
9. Look at the if verb = "drop" statement. Why does the for loop check if key = noun and val == 99?

• Adventure Game 1
• Adventure Game 2: Add Objects
• => Adventure Game 3: Take and Drop Objects
• Adventure Game 4: Structured Programming
• Adventure Game 5: Adding New Commands and Tidying Old Ones
• Adventure Game 6: Using Objects
• Adventure Game 7: Robust Code
• Adventure Game 8: Making a Playable Game