variables, references and data structures

COMP 1001: Introduction to Computers for Arts and Social Sciences

Making Stories Interactive

Variables, References and Data Structures


Learning Objectives

• Learn how information is stored on a computer.

• Learn basic programming concepts (variables, if statements, loops, and

functions) and write simple programs using these concepts.


What is a Story?


ACTORS perform actions

THE WORLD changes

EVENTS relate to each other


About people, not things STORIES:

conflict


Interactivity


Two or more agents

Understand each other

Respond properly


Tools


http://twinery.org/

http://twinery.org/


http://www.inklestudios.com/inklewriter/

http://www.inklestudios.com/inklewriter/


http://www.renpy.org/

http://www.renpy.org/


From the Beginning…


We will examine how to do a simple text-based interactive story.


User Input

We want to ask the user a question.

print("Choose from the following options:")

print("1: go left")

print("2: go right")

input("> ")


User Input

We want to ask the user a question.

print("Choose from the following options:")

print("1: go left")

print("2: go right")

input("> ") This function returns an answer. Where should we put it?


Variables

A variable is like a box we can put information in.


answer = input("> ")

answer

2

Variables

The user types 2 and presses enter.


answer = input("> ")

answer

Variables

The value is stored in the box.

2


if answer == 2:

print("You chose to go left, ")

print(" a most dangerous path.")

answer

2

Variables


if answer == 2:

print("You chose to go left, ")

print(" a most dangerous path.")

answer

2

Variables

Look at what's inside the box and

do something with it


x = 0

while x < 2:

x = x + 1

x

0

Variables


x = 0

while x < 2:

x = x + 1

x

0

Variables

Put zero in a box labelled x.


x = 0

while x < 2:

x = x + 1

x

0

Variables

Peek in the box to get the value…


x = 0

while x < 2:

x = x + 1

x

0

Variables

…and compare it to 2


x = 0

while x < 2:

x = x + 1

x

0

Variables

Peek in the box to get the value…


x = 0

while x < 2:

x = x + 1

x

1

Variables

…add 1 to it…


x = 0

while x < 2:

x = x + 1

x

1

Variables

…and put the result back into the box


x = 0

while x < 2:

x = x + 1

x

Variables

Now the box contains the value 1.

1


What is the value of y after the execution of this code? x = 37

y = x + 2

x = 20

Text 37607 1052115: 39 1052116: 22 1052117: 59 1052118: 20 1052119: 57


Data Types

We know there are different ways of representing data in memory using binary

numbers.


Data Types

Name Type

int plain integer – no decimal point

float floating point number – has a decimal point

complex real + imaginary parts

string text between quotes


Data Types

We know there are different ways of representing data in memory using binary

numbers.

How does our variable know what type of data it is storing?


Data Types

Answer: Context.

Variable Data Type

a = 3 integer

a = 3.4 float

a = "3.4" string

a = 0b11 integer

a = "0b11" string


Stories as Data


Storing Story Data We'll represent a short story based on the classic nursery

rhyme Little Miss Muffet:

Little Miss Muffet sat on her tuffet Eating her curds and whey When along came a spider And sat down beside her

And scared Miss Muffet away

http://crown-heart.deviantart.com/art/Little-Miss-Muffet-162099928


1. The sun shone brightly when Miss Muffet finally arrived at her favorite tuffet. Though it seemed odd to others that she’d decide to store any furniture outdoors, Miss Muffet loved sitting on the footstool under her favorite tree.

2. Just like every morning, Miss Muffet was famished. Luckily, just like every morning, she had brought her curds and whey to enjoy for breakfast.

3. As Miss Muffet brought the first spoonful to her mouth, a very long-legged but otherwise friendly spider noticed her sitting below. The spider headed downward, released his thread above him, so he could visit the curious creature now seated under his tree.

4. As the spider landed on Miss Muffet’s spoon, the girl sensed something was wrong. As soon as she saw the insect, she screamed before she could even consider that she was, in fact, facing a friendly spider.

5. Miss Muffet was gone before the spider could even say hello. The spider felt terrible for scaring her away, but soon forgot as he investigated the curds and whey left behind.


1. The sun shone brightly when Miss Muffet finally arrived at her favorite tuffet. Though it seemed odd to others that she’d decide to store any furniture outdoors, Miss Muffet loved sitting on the footstool under her favorite tree.

2. Just like every morning, Miss Muffet was famished. Luckily, just like every morning, she had brought her curds and whey to enjoy for breakfast.

3. As Miss Muffet brought the first spoonful to her mouth, a very long-legged but otherwise friendly spider noticed her sitting below. The spider headed downward, released his thread above him, so he could visit the curious creature now seated under his tree.

4. As the spider landed on Miss Muffet’s spoon, the girl sensed something was wrong. As soon as she saw the insect, she screamed before she could even consider that she was, in fact, facing a friendly spider.

5. Miss Muffet was gone before the spider could even say hello. The spider felt terrible for scaring her away, but soon forgot as he investigated the curds and whey left behind.

What data type do we need, and how will we store these values?


Data Structures

Used to organize information on a computer so it can be

used efficiently for the task at hand


The List Data Structure



These numbers are called indexes



Computer scientists count from zero


Index Scene

0

The sun shone brightly when Miss Muffet finally arrived at her

favorite tuffet. Though it seemed odd to others that she’d decide

to store any furniture outdoors, Miss Muffet loved sitting on the

footstool under her favorite tree.

1

Just like every morning, Miss Muffet was famished. Luckily, just

like every morning, she had brought her curds and whey to enjoy

for breakfast.

2

As Miss Muffet brought the first spoonful to her mouth, a very

long-legged but otherwise friendly spider noticed her sitting

below. The spider headed downward, released his thread above

him, so he could visit the curious creature now seated under his

tree.

3

As the spider landed on Miss Muffet’s spoon, the girl sensed

something was wrong. As soon as she saw the insect, she

screamed before she could even consider that she was, in fact,

facing a friendly spider.

4

Miss Muffet was gone before the spider could even say hello. The

spider felt terrible for scaring her away, but soon forgot as he

investigated the curds and whey left behind.


Lists in Python

Creating a list:

[5, 3, -2, 10]


Lists in Python

Creating a list:

[1, -9.5555, "hello", [1, 2, 3]]


Lists in Python

Creating a list:

[1, -9.5555, "hello", [1, 2, 3]]

Lists can contain multiple data types – even other

lists!


Lists in Python

Assigning a list to a variable:

myList = [1, -9.5555, "hello", [1, 2, 3]]


Lists in Python

Accessing items in a list:

myList = [1, -9.5555, "hello", [1, 2, 3]]

print(myList[2])


Lists in Python

Accessing items in a list:

myList = [1, -9.5555, "hello", [1, 2, 3]]

print(myList[2])

Prints "hello"


Lists in Python

Getting the length of a list:

len(myList)


Lists in Python


print(myList[len(myList)-1])


Lists in Python


print(myList[len(myList)-1])

Prints the last item in the list (remember, starts at

zero!)


Lists in Python


print(myList[-1])

Shortcut for accessing last item in the list


missMuffetScenes = [

"The sun shone brightly…",

"Just like every morning…",

"As Miss Muffet brought…",

"As the spider landed on…",

"Miss Muffet was gone…"

]

Scene text abbreviated for space…


Printing List Items

How can we print out our story scenes?


Printing List Items

print(missMuffetScenes[0])






Printing List Items






Is this really going to work for longer stories?


While Loop

Drive the track while the race is not over


Printing List Items

currentIndex = 0

while currentIndex <= 4:

print(missMuffetScenes[currentIndex])

currentIndex = currentIndex + 1


Printing List Items

currentIndex = 0




We want the first index to give us the first scene

in the list


Printing List Items

currentIndex = 0




Drive laps so long as we haven't gone past the

last item


Printing List Items

currentIndex = 0




Should use len(missMuffetScenes)-1


Printing List Items

currentIndex = 0




Drive the lap is printing the scene…


Printing List Items

currentIndex = 0




…and updating the index to get ready for the next lap


For Loop

Drive the track one lap for every item in a list


For Loop

for <variableName> in <listName>:

<code to run a number of times

equal to the size of the list>


Printing List Items

for scene in missMuffetScenes:

print(scene)


Printing List Items


print(scene)

The list that we will be looping over


Printing List Items


print(scene)

This variable will get a new value from the list every lap


Printing List Items


print(scene)

Driving the lap is just printing this time – everything else is

updated automatically


Things to Do With Scene Lists

Useful in video games, when players can explore the world in

between scenes.

Allows us to rearrange the ordering of the scenes.


Rearranging List Items

Lists can be rearranged with a series of swaps.



Swapping the first and last items…

missMuffetScenes[-1] = missMuffetScenes[0]

missMuffetScenes[0] = missMuffetScenes[-1]






!!!





Get the contents of the first box…





…and put them into the last box





Now we're just copying scene1 back into the first box




temp = missMuffetScenes[-1]


missMuffetScenes[0] = temp






First put scene3 into the temporary box






Then we can copy scene1 to the last box before copying scene3 into the first box (now

shown)


What is the value of a after the execution of this code? a = [2, 4, 6, 8]

a.remove(4) #item

a.pop(2) #index

Text 37607 622977: [2,4] 622997: [6,8] 622998: [2,6] 622999: [2,8] 623000: Nothing / error


What is printed by this code? lst = [3, 6, 9]

sum = 0

counter = 0

while counter < len(lst):

sum += counter

counter += 2

print(sum)

Text 37607 634005: 18 634007: 6 634014: 2 634015: 9 634021: Nothing / error


Branching Stories


This is a tree data structure


As the spider landed on Miss Muffet’s spoon, the girl sensed something was wrong. Miss Muffet should run away as soon as she sees the spider. Miss Muffet should stay to greet the spider.


As the spider landed on Miss Muffet’s spoon, the girl sensed something was wrong. As soon as she saw the insect, she screamed before she could even consider that she was, in fact, facing a friendly spider. Miss Muffet was gone before the spider could even say hello. The spider felt terrible for scaring her away, but soon forgot as he investigated the curds and whey left behind.

The End


As the spider landed on Miss Muffet’s spoon, the girl sensed something was wrong. Miss Muffet should run away as soon as she sees the spider. Miss Muffet should stay to greet the spider.


When she saw the spider, curiosity got the best of her. “Why hello, there, little friend!” she said. Offer the spider some curds and whey. Don’t share with the spider.


When she saw the spider, curiosity got the best of her. “Why hello, there, little friend!” she said. Miss Muffet held out her spoon as the wide-eyed spider grinned and lunged for the delicious snack. From that day forward, the spider joined Miss Muffet every morning for breakfast with his new friend.

The end


When she saw the spider, curiosity got the best of her. “Why hello, there, little friend!” she said. Offer the spider some curds and whey. Don’t share with the spider.


When she saw the spider, curiosity got the best of her. “Why hello, there, little friend!” she said. Although Miss Muffet tried to make small talk with the spider, he was a little put off by her unwillingness to share. The spider decided he’d try another tree to see if he could find someone a little more generous with their breakfast. Miss Muffet never saw him again.

The end


How can we represent a scene as data?


How can we represent a scene as data?

We need: - The text of a scene - Scenes that either offer a choice or don't - For scenes that do offer a choice, the text

for the options - What scene to go to next (automatically or

based on choice)


[False,

"Just like every morning, Miss Muffet was

famished. Luckily, just like every morning, she

had brought her curds and whey to enjoy for

breakfast.",

"SpoonMouth"]


[False,




breakfast.",

"SpoonMouth"]

There are no choices in this scene.


[False,




breakfast.",

"SpoonMouth"] All scenes have their scene text to print


[False,




breakfast.",

"SpoonMouth"] This is the next scene to visit


[True,

" As the spider landed on Miss Muffet’s spoon,

the girl sensed something was wrong.",

"Miss Muffet should run away as soon as she sees

the spider.",

"RunAway",

"Miss Muffet should stay to greet the spider.",

"Stay"]


[True,




the spider.",

"RunAway",


"Stay"]

This scene does have a choice


[True,




the spider.",

"RunAway",


"Stay"]

Scene text


[True,




the spider.",

"RunAway",


"Stay"]

Option 1


[True,




the spider.",

"RunAway",


"Stay"]

Next scene if option 1 is chosen


[True,




the spider.",

"RunAway",


"Stay"]

Option 2


[True,




the spider.",

"RunAway",


"Stay"] Next scene if

option 2 is chosen


Now we have scene data – how can we associate the

scene name with the data?


Dictionaries

The dictionary data structure associates one piece of data with

another.


Dictionaries

myDictionary = {"one" : 1, "two" : 2, "three" : 3}

Creating a new dictionary:


Dictionaries



Keys

(similar to words in a dictionary to look up)


Dictionaries



Values

(similar to the definition found when looking up the word)


Dictionaries




Dictionaries

print(myDictionary["two"])

Accessing values in a dictionary:


Dictionaries

print(myDictionary["two"])

Accessing values in a dictionary:

Prints 2


Dictionaries

myDictionary["two"] = 22

Replacing values in a dictionary:


Dictionaries

myDictionary["ten"] = 10

Adding new values to a dictionary:


Dictionaries

for key in myDictionary.keys():

print(myDictionary[key])

Printing values in a dictionary:

for value in myDictionary.values():

print(value)

print(list(myDictionary.keys()))

print(list(myDictionary.values()))


What is the value of d after this code runs? d = {3:4, 4:5, 5:6}

d[3] = 8

d[6] = 7

Text 37607 729146: {3:4, 4:5, 5:8} 729147: {3:8, 4:5, 5:6} 729151: {3:4, 4:5, 5:8, 6:7} 729152: {3:8, 4:5, 5:6, 6:7} 729153: Nothing / error


References


A Look at Our Data's Structure

variables, references and data structures

Documents