This is a programming project I undertook with my 13 year old son. Madlibs is a story game for kids: a story is written and a few dozen important words are taken out, replaced by blanks. The blanks are labelled with their part of speech or other category ("noun", "adjective", "an animal", and so on). One kid reads out the categories, another kid (or kids) supply new words without knowing the story. When all the blanks have been filled in, the story is read out, usually with comic results.

(For more about how we chose Madlibs as a subject, see my blog entry Programming with kids: Madlibs.)

The first program

I started by talking with my son about how the program would have to work. We talked about the structure of the story itself. It was a list of things. He said there were two types of things: static pieces and dynamic pieces. We talked about how a story was constructed: by looking at each piece in turn.

"And what should it do with each piece?" The first idea was that for static pieces, print the text, and for dynamic pieces, print the category and collect an answer. Son realized that this would expose the story as it went along, before the questions were answered. Here he was stuck.

I explained that we could build up the story in memory, and print the whole thing at the end. Eventually, we sat down at the computer and created this program:

""" The awesome Madlib program.
"""

import sys, textwrap

def get_input(prompt):
    print "%s> " % prompt,
    return sys.stdin.readline().strip()

storylist = [
    ('static', "Once upon a time there was a "),
    ('dynamic', "an adjective"),
    ('static', ", "),
    ('dynamic', "another adjective"),
    ('static', " "),
    ('dynamic', "an animal"),
    ('static', ". He liked to "),
    ('dynamic', "a verb in the present tense"),
    ('static', " all day. One day, he went to "),
    ('dynamic', "an adjective"),
    ('static', " "),
    ('dynamic', "a place"),
    ('static', " to meet "),
    ('dynamic', "a person"),
    ('static', "."),
    ]

story = ""

def dynamic(kind):
    return get_input("give me " + kind)

for thing in storylist:
    if thing[0] == 'static':
        story += thing[1]
    elif thing[0] == 'dynamic':
        story += dynamic(thing[1])
    else:
        print "Huh? What's %s?" % thing[0]

print ""
print textwrap.fill(story)

I supplied the tricky parts (get_input, and the textwrap business), and suggested the technique of making the story list be a list of tuples. But my son did a lot of the thinking through what had to happen. The "dynamic" function is there because he wanted to use a function.

This program worked, and was a source of much joy. It did something interesting, and my son eagerly encouraged everyone to try it out. He really seemed pleased by the work he had done, and I was pleased that we could talk through some of the coding challenges and find answers together.

The object-oriented version

The first change my son wanted to make was to have the program ask the questions in a random order, so that the player had less chance of second-guessing the intent of the author. I had imagined a number of ways to expand on the program, but this wasn't one of them, so I was psyched: the Madlibs genre was going to be a fertile one!

In preparation for the feature, I thought it would be good to get us onto a more modern architectural foundation. I explained about classes and objects, and refactored our program into this:

""" The awesome Madlib program.
"""

import sys, textwrap

def get_input(prompt):
    print "%s> " % prompt,
    sys.stdout.softspace = 0
    return sys.stdin.readline().strip()

class static:
    def __init__(self, text):
        self.text = text

    def getStoryPiece(self):
        return self.text

class dynamic:
    def __init__(self, prompt):
        self.prompt = prompt

    def getStoryPiece(self):
        return get_input("give me " + self.prompt)

storylist = [
    static("Once upon a time there was a "),
    dynamic("an adjective"),
    static(", "),
    dynamic("another adjective"),
    static(" "),
    dynamic("an animal"),
    static(". He liked to "),
    dynamic("a verb in the present tense"),
    static(" all day. One day, he went to "),
    dynamic("an adjective"),
    static(" "),
    dynamic("a place"),
    static(" to meet "),
    dynamic("a person"),
    static("."),
    ]

story = ""

for thing in storylist:
    story += thing.getStoryPiece()

print ""
print textwrap.fill(story)

There was a side discussion that didn't survive in the code. I showed how to use the same storylist variable two ways, first to play dynamically, with the program asking questions and producing the finished story, and second to play on paper, with the program printing a play sheet suitable for use with pencil and paper.

Random questioning

To do the random questioning, we'll need to split the main loop into two passes: one to get the dynamic pieces, shuffle them, and get the answers, then another to build the story. The dynamic pieces will have to store their answers between the two passes.

To store the answers, we talked about member variables. We had used them to store the prompt before, but the __init__ methods seem formal and uninteresting, and their values are constants. It wasn't until we got to prompting the user and storing the answer in a member variable that we were really talking about variables.

Here's the third version of the program. We make two passes over the list, first to collect the pieces that ask questions. Then we shuffle that list and have each slot ask its question. Then we walk the whole story from beginning to end building the finished story. It's important to understand the relationship between a list and the objects it contains. The two lists point at the same objects, otherwise the program wouldn't work.

""" The awesome Madlib program.
"""

import random, sys, textwrap

def get_input(prompt):
    answer = ''
    while not answer:
        print "%s> " % prompt,
        sys.stdout.softspace = 0
        answer = sys.stdin.readline().strip()
    return answer

class static:
    def __init__(self, text):
        self.text = text

    def readStoryPiece(self):
        return self.text

class dynamic:
    def __init__(self, prompt):
        self.prompt = prompt

    def readStoryPiece(self):
        return self.answer

    def askUser(self):
        self.answer = get_input("give me " + self.prompt)

storylist = [
    static("Once upon a time there was a "),
    dynamic("an adjective"),
    static(", "),
    dynamic("an adjective"),
    static(" "),
    dynamic("an animal"),
    static(". He liked to "),
    dynamic("a verb"),
    static(" all day. One day, he went to "),
    dynamic("an adjective"),
    static(" "),
    dynamic("a place"),
    static(" to meet "),
    dynamic("a person"),
    static("."),
    ]

story = ""

dynamiclist = []
for thing in storylist:
    if isinstance(thing, dynamic):
        dynamiclist += [thing]

random.shuffle(dynamiclist)

# Pass one: fills in the words.
for thing in dynamiclist:
    thing.askUser()

# Read the story in order.
for thing in storylist:
    story += thing.readStoryPiece()

print ""
print textwrap.fill(story)

Now the program asks for words in random order, making it more difficult for the player to second-guess how his words will be used.

Re-usable slots

The next feature to tackle was re-usable slots. For example, after asking for "an adjective", the word could be used twice or more in the same story. To make this work, we had to expand the types of objects in the storylist. We could have gone two different ways: add two new objects (one for the reusable word, and one for where it was reused), or add just one new object (the reused word) while expanding the dynamic slot to be reusable. Son decided to go the four-object route.

We also had to introduce the concept of dictionaries, so we could name and store the reusable words:

""" The awesome Madlib program.
"""

import random, sys, textwrap

def get_input(prompt):
    answer = ''
    while not answer:
        print "%s> " % prompt,
        sys.stdout.softspace = 0
        answer = sys.stdin.readline().strip()
    return answer

class static:
    def __init__(self, text):
        self.text = text

    def readStoryPiece(self):
        return self.text

class dynamic:
    def __init__(self, prompt):
        self.prompt = prompt

    def readStoryPiece(self):
        return self.answer

    def askUser(self):
        self.answer = get_input("give me " + self.prompt)


class reusable:
    def __init__(self, prompt, callname):
        self.prompt = prompt
        self.callname = callname

    def readStoryPiece(self):
        return self.answer

    def askUser(self):
        self.answer = get_input("give me " + self.prompt)
        reusables[self.callname] = self.answer

class reuser:
    def __init__(self, callname):
        self.callname = callname

    def readStoryPiece(self):
        return reusables[self.callname]

storylist = [
    static("Once upon a time there was a "),
    reusable("an adjective", "adj1"),
    static(" "),
    dynamic("a noun"),
    static(". It was really "),
    reuser("adj1"),
    static(". It liked to "),
    dynamic("a verb"),
    static(" all day. One day, it went to "),
    dynamic("a place"),
    static(" to meet "),
    dynamic("a person"),
    static(". To get there, it rode in a "),
    reusable("a vehicle", "n1"),
    static(", but on the way there, the "),
    reuser("n1"),
    static(" crashed. It had to walk the rest of the way.")
    ]

story = ""

reusables = {}

asklist = []
for thing in storylist:
    if hasattr(thing, 'askUser'):
        asklist += [thing]

random.shuffle(asklist)

# Pass one: fills in the words.
for thing in asklist:
    thing.askUser()

# Read the story in order.
for thing in storylist:
    story += thing.readStoryPiece()

print ""
print textwrap.fill(story)

The end result works well, and everyone (mom, brothers, and so on) were pleased with the results. Stylistically, the reusable and dynamic classes are too similar. Eventually I'll probably encourage a refactoring to reduce the duplication.

One interesting feature was how we chose the pieces to shuffle and use in the first pass. Originally, the code was:

dynamiclist = []
for thing in storylist:
    if isinstance(thing, dynamic):
        dynamiclist += [thing]
    elif isinstance(thing, reusable):
        dynamiclist += [thing]

Son asked if we could combine the two clauses (good instinct!). So we simplified it to:

dynamiclist = []
for thing in storylist:
    if isinstance(thing, dynamic) or isinstance(thing, reusable):
        dynamiclist += [thing]

and then, using isinstance more cleverly, to:

dynamiclist = []
for thing in storylist:
    if isinstance(thing, (dynamic, reusable)):
        dynamiclist += [thing]

This isn't bad, but I took the opportunity to advocate encapsulation and polymorphism. The fewer places we talk explicitly about classes, the more flexible the code will be. I pointed out that the only thing we did with the elements of dynamiclist was to call askUser on it, so why not just pick out the things that have an askUser method. Along the way, we changed the name to asklist to better reflect what it's doing:

asklist = []
for thing in storylist:
    if hasattr(thing, 'askUser'):
        asklist += [thing]

External story files

The last feature was storing the story in an external file. This makes it possible to edit the story without changing the program, and allows us to have a number of stories we can choose from at run time.

The story is stored in a text file, usually with a file extension of .mad (the boy was very excited about having our own file extension!). For example:

story1.mad

Once upon a time there was a [ an adjective : adj1 ] [ a noun ].
It was really [:adj1].  It liked to [ a verb ] all day. One day,
it went to [ a place ] to meet [ a person ]. To get there, it
rode in a [ a vehicle:n1 ], but on the way there, the [:n1]
crashed.  It had to walk the rest of the way.

The text is used verbatim. Slots are in square brackets, with the prompt inside them. A colon indicates the internal name of the value provided, which can be reused by a slot with no prompt, just a value name.

Here's the next version of the madlib code:

""" The awesome Madlib program.
"""

import random, sys, textwrap

def get_input(prompt):
    answer = ''
    while not answer:
        print "%s> " % prompt,
        sys.stdout.softspace = 0
        answer = sys.stdin.readline().strip()
    return answer

class static:
    def __init__(self, text):
        self.text = text

    def readStoryPiece(self):
        return self.text

class dynamic:
    def __init__(self, prompt, callname=None):
        self.prompt = prompt
        self.callname = callname

    def readStoryPiece(self):
        return self.answer

    def askUser(self):
        self.answer = get_input("give me " + self.prompt)
        if self.callname:
            reusables[self.callname] = self.answer

class reuser:
    def __init__(self, callname):
        assert type(callname) == type("")
        self.callname = callname

    def readStoryPiece(self):
        return reusables[self.callname]

def getStoryFile():
    return open(get_input("give me the story file")).read()

def getStoryPieces():
    story = getStoryFile()
    startpos = 0
    while 1:
        bracket = story.find("[", startpos)
        if bracket == -1:
            break
        storylist.append(static(story[startpos:bracket]))
        endbracket = story.find("]", bracket)
        if endbracket == -1:
            break
        startpos = endbracket + 1
        dynamicpart = story[bracket+1:endbracket]
        dynamicpieces = dynamicpart.split(":")
        dynamiclength = len(dynamicpieces)
        if dynamiclength == 1:
            storylist.append(dynamic(story[bracket+1:endbracket].strip()))
        elif dynamicpart.find(":") == 0:
            storylist.append(reuser(dynamicpieces[1].strip()))
        else:
            storylist.append(dynamic(dynamicpieces[0].strip(),dynamicpieces[1].strip()))

    storylist.append(static(story[startpos:]))


storylist = []

getStoryPieces()

story = ""
reusables = {}

asklist = []
for thing in storylist:
    if hasattr(thing, 'askUser'):
        asklist += [thing]

random.shuffle(asklist)

# Pass one: fills in the words.
for thing in asklist:
    thing.askUser()

# Read the story in order.
for thing in storylist:
    story += thing.readStoryPiece()

print
print textwrap.fill(story)

The getStoryPieces function does the work of reading the text format. This could probably be cleaned up, but it works. We had to do a lot of careful thinking about where in the string each variable pointed, and about the different forms of slots the parser might encounter. Personally, I would have made the story file name be an argument on the command line, but the son liked prompting better, so prompting it is. Here's a sample run:

$ madlib.py
give me the story file> story1.mad
give me a verb> juggle
give me a place> Royal Albert Hall
give me a person> Alfred E. Neuman
give me an adjective> lumpy
give me a vehicle> unicycle
give me a noun> grapefruit

Once upon a time there was a lumpy grapefruit. It was really lumpy.
It liked to juggle all day. One day, it went to Royal Albert Hall to
meet Alfred E. Neuman. To get there, it rode in a unicycle, but on the
way there, the unicycle crashed.  It had to walk the rest of the way.

More to come?

I think we are probably done with madlibs, but there are more possibilities for future work that we've talked about:

  • Having the program choose randomly among a number of such stories (requires directory operations).
  • Smarter text manipulation, for example, a dynamic piece that knows its answer has to be capitalized because it appears at the start of a sentence, or a piece that can supply the proper article ("a" or "an") depending on the word supplied by the player.
  • What about a kind of dynamic piece that has a built-in list of choices, and the program chooses among them itself? This would give the story a little more randomness, without having to ask another question.

I really liked this project: it has enough interest to keep the son motivated, but is simple enough that an hour or two of talking and typing produced an interesting result.

See also

  • My blog, where other similar topics are occasionally discussed.

Comments

[gravatar]
Gary Bishop 10:43 AM on 1 Aug 2005

Thanks for writing this up! A fine idea.

[gravatar]
Calvin Spealman 12:54 PM on 10 Aug 2005

I really like reading this on going story. Although I do not have children of my own yet, my wife and I plan to, and this is a very encouraging thing to read. I'd love to be able to share my technical passions with a son (or daughter). Of course, even though we may begin a family in the near future, it would be some where in the order of a decade before I could begin this sort of father-child pasttime. It makes me wonder how much will change in that time, and how many "When I Was Your Age" stories it will bring out of me. God, I feel so old already.

I find myself reading this code and saying to myself "shouldn't do that like that" or "it would be better to ...", and then stopping myself saying "Just a guy teaching his kid, so its fine." Then , I realize how little need such a program has for such optimizations. It is a refreshing feeling, because seldom does code actually tend one away from premature optimization, we're usually everywhere for where to do it. Just a technical comment along with the more personal one.

Enjoying the story, keep at it.

[gravatar]
Blake Winton 1:42 PM on 10 Aug 2005

As a text format for the stories, when you get to the "Reading stories in from a text file", might I suggest the following:

<prompt> is a dynamic with a prompt of "prompt", <prompt|callname> is a reusable with a callname of "callname", and <|callname> is a reuser of "callname".

I think it would be fairly easy to read and write, and the chances that you would want to use < or > in a story are slim. Ditto for using | in a prompt...
I have no idea how hard it would be to parse, but hey, that's the fun of it, right? ;)

(Pity there's no preview. Please delete my previous comment.)

[gravatar]
Nate Finch 4:48 PM on 10 Aug 2005

Ned, you totally need sample output here! :) BTW, very cool project - I hadn't thought it through but this seems like a great initial introduction to programming. Being able to make a functional program in just a few lines, and then being able to iteratively make it more complicated and more interesting is a great learning experience.

[gravatar]
Anonymous 5:17 PM on 30 Aug 2010

I have written a madlib program before, in QBASIC. It had a similar function.

Add a comment:

name
email
Ignore this:
not displayed and no spam.
Leave this empty:
www
not searched.
 
Name and either email or www are required.
Don't put anything here:
Leave this empty:
URLs auto-link and some tags are allowed: <a><b><i><p><br><pre>.