## – List Solutions

``````breakfast = ["Sausage", "Eggs", "Beans", "Bacon", "Tomatoes", "Mushrooms"]
palindromic = ["Sausage", "Eggs", "Beans", "Beans", "Eggs", "Sausage"]
nums = [1,1,3,3,3,2,2,2,1,1,1,1,4,4,4,4]
letters = ['a', 'a', 'a', 'a', 'b', 'c', 'c', 'a', 'a', 'd', 'e', 'e', 'e', 'e']

def print_list(list):
for item in list:
print(item)

def last_element(list):
return (list[-1])

def last_but_one(list):
return (list[-2])

# Using reversed function
def my_reverse(list):
new_list = []
for item in reversed(list):
new_list.append(item)
return new_list

# Using for loop
def my_reverse2(list):
new_list = []
for i in range (len(list)-1, -1, -1):
new_list.append(list[i])
return new_list

# Using list comprehension
def my_reverse3(list):
return [item for item in reversed(list)]

# Using slicing
def my_reverse4(list):
return list[::-1]

def is_palindrome(list):
if list == my_reverse(list):
return True
else:
return False

def compress(list):
new_list = []
last_item = list[0] + 1 # so first number is different to itself
for num in list:
if num != last_item:
new_list.append(num)
last_item = num
return new_list

def pack(list):
pack_list = []
last_item = list[0]
word = ""
for item in list:
if item == last_item:
word = word + item
else:
pack_list.append(word)
word = item
last_item = item
pack_list.append(word)
return pack_list
``````

## 3: Lists

### 3.1 Print List

Write a function that prints out a list, one element per line

#### 3.1.1 Example

``` 1: breakfast = ["Sausage", "Eggs", "Beans", "Bacon", "Tomatoes", "Mushrooms"]
2:
3: print_list(breakfast)
4:  *** Output ***
5: Sausage
6: Eggs
7: Beans
8: Bacon
9: Tomatoes
10: Mushrooms
```

### 3.2 Last Element of Array

Write a function that returns the last element of a string array

#### 3.2.1 Example

```1: breakfast = ["Sausage", "Eggs", "Beans", "Bacon", "Tomatoes", "Mushrooms"]
2:
3: print(last_element(breakfast));
4:  *** Output ***
5: Mushrooms
```

### 3.3 Last But One Element of Array

Write a function that returns the last but one element of a string array

#### 3.3.1 Example

```1: breakfast = ["Sausage", "Eggs", "Beans", "Bacon", "Tomatoes", "Mushrooms"]
2:
3: print(last_but_one(breakfast));
4:  *** Output ***
5: Tomatoes
```

### 3.4 Reverse a list, leaving original intact

Return a list in reverse order, while leaving the original list intact.

#### 3.4.1 Example

``` 1: breakfast = ["Sausage", "Eggs", "Beans", "Bacon", "Tomatoes", "Mushrooms"]
2:
3: print(my_reverse(breakfast))
4: print(breakfast)
5:  *** Output ***
6: : Mushrooms
7: : Tomatoes
8: : Bacon
9: : Beans
10: : Eggs
11: : Sausage
12: : Sausage
13: : Eggs
14: : Beans
15: : Bacon
16: : Tomatoes
17: : Mushrooms
```

### 3.5 Palindromic lists

Write a function that tests to see if a list is palindromic, i.e. the elements are the same when reversed.

#### 3.5.1 Example

```1: palindromic = ["Sausage", "Eggs", "Beans", "Beans", "Eggs", "Sausage"]
2: breakfast = ["Sausage", "Eggs", "Beans", "Bacon", "Tomatoes", "Mushrooms"]
3:
4: print(is_palindrome(palindromic))
5: print(is_palindrome(breakfast))
6:  *** Output ***
7: True
8: False
```

### 3.6 Consecutive Duplicates

Write a function to print out list of integers with consecutive duplicates eliminated

```1: nums = [1,1,3,3,3,2,2,2,1,1,1,1,4,4,4,4]
2:
3: compress(nums)
4:  *** Output ***
5: : 1
6: : 3
7: : 2
8: : 1
9: : 4
```

### 3.7 Pack Duplicates

Pack consecutive duplicates of a char list into Strings

```1: letters = ['a', 'a', 'a', 'a', 'b', 'c', 'c', 'a', 'a', 'd', 'e', 'e', 'e', 'e']
2:
3: pack(letters)
4:  *** Output ***
5: : aaaa, b, cc, aa, d, eeee
```

## Adventure Game 8: Making a Playable Game

Now we have a working game engine, we need to make the game more interesting.

We can do this in a number of ways.

1. Think of an interesting setting: in a castle, on a spaceship, in a school for witches and wizardsâ€¦
2. What quest are we setting the player? To find the gold? Escape from the space station before it explodes? To find the spy?
4. What sort of objects could we use? Magic wands, rayguns, teleporters?
5. What sort of puzzles and riddles could we add?

## Exercise

1. Think of the setting for your game. What does the player have to do (what’s their quest?)
2. Draw a map for your game (see lesson 1 for an example) Don’t add too many locations – 16 is more then enough.
3. Think of the objects the player will have to use and add them to the map.
4. Make a note of the game play. What will the player have to do to complete the game.
5. Now modify the code of the game engine to write your own game.
6. Get your partner to play the game and feedback.
7. Make any improvements to the game.

## Adventure Game 7: Robust Code

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 spoon
Traceback (most recent call last):
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}]
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 6: Using Objects

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}]
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.

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}]
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 printobjects() 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 4: Structured Programming

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}]
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 3: Take and Drop Objects

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}]
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?

Now we have the locations sorted, we need to add objects to the game. These will be things such as keys and chests. Later on we’ll add code so that the player can use these objects

Note how I’m only using 3 locations while I write this game. It’s always a good idea to keep things simple. Get the mechanics of the game working first, and then expand it.

Copy and paste the code below 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}]
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?")
if ans in moves[location]:
location = moves[location].get(ans)
print(places[location])
print_objects()
else:
print("I can't move that way")

Main()``````

## Exercise

1. Look at the objects dictionary `objects = {“spanner”:0, “lockpick”:0, “spade”:2}`. What do the keys in the dictionary represent? (hint: the key is the part before the colon:)
2. What do the values in the dictionary represent?
3. Add “rope” to the list of objects. Place it in the cave.
4. Add “torch” to the list of objects. Place it in the cabin.
5. Run the code and check the objects are where you think they should be.
6. Look at the print_objects() function. Explain how it works

### Extension

1. Draw your own map for a game. Implement it. Modify the code so that you are using your map.
3. Add code so that if the user types “l” (for look) the game prints out the current location and a list of objects.

• Moving around three locations

Copy the following code into your IDE and run it.

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

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

while ans != "bye":
ans = input("What now?")
if ans in moves[location]:
location = moves[location].get(ans)
print(places[location])
else:
print("I can't move that way")

Main()
```

## Exercise

1. How do you exit the game?
2. What sort of data structure has been used to store the places?
3. What sort of data structure has been used to store the moves?
4. What does the variable location do?
5. Give some valid moves.
6. How does the code check if a move is valid?
7. Which line of code sets the new location?
8. Look at the map below. Add the extra locations to the game.
9. Run the code and check that it works.