Exercise 41: Gothons From Planet Percal #25

Did you figure out the secret of the function in the dict from the last exercise? Can you explain it to yourself? I'll explain it and you can compare your explanation with mine. Here are the lines of code we are talking about:

cities['_find'] = find_city
city_found = cities['_find'](cities, state)

Remember that functions can be variables too. The def find_city just makes another variable name in your current module that you can use anywhere. In this code first we are putting the function find_city into the dict cities as '_find'. This is the same as all the others where we set states to some cities, but in this case it's actually the function.

Alright, so once we know that find_city is in the dict at _find, that means we can do work with it. The 2nd line of code (used later in the previous exercise) can be broken down like this:

1. Python sees city_found = and knows we want to make a new variable.
2. It then reads cities and finds that variable, it's a dict.
3. Then there's ['_find'] which will index into the cities dict and pull out whatever is at _find.
4. What is at ['_find'] is our function find_city so Python then knows it's got a function, and when it hits ( it does the function call.
5. The parameters cities, state are passed to this function find_city, and it runs because it's called.
6. find_city then tries to look up states inside cities, and returns what it finds or a message saying it didn't find anything.
7. Python takes what find_city returned, and finally that is what is assigned to city_found all the way at the beginning.

Here's a trick. Sometimes these things read better in English if you read the code backwards. This is how I would do it for that same line (remember backwards):

1. state and cities are...
2. passed as parameters to...
3. a function at...
4. '_find' inside...
5. the dict cities...
6. and finally assigned to city_found.

Here's another way to read it, this time "inside-out".

1. Find the center item of the expression, in this case ['_find'].
2. Go counter-clock-wise and you have a dict cities, so this finds the element _find in cities.
3. That gives us a function. Keep going counter-clock-wise and you get to the parameters.
4. The parameters are passed to the function, and that returns a result. Go counter-clock-wise again.
5. Finally, we are at the city_found = assignment, and we have our end result.

After decades of programming I don't even think about these three ways to read code. I just glance at it and know what it means. I can even glance at a whole screen of code, and all the bugs and errors jump out at me. That took an incredibly long time and quite a bit more study than is sane. To get that way, I learned these three ways of reading most any programming language:

1. Front to back.
2. Back to front.
3. Counter-clock-wise.

Try them out when you have a difficult statement to figure out.

Now type in your next exercise, then go over it. This one is gonna be fun.

from sys import exit
from random import randint

def death():
    quips = ["You died.  You kinda suck at this.",
             "Nice job, you died ...jackass.",
             "Such a luser.",
             "I have a small puppy that's better at this."]

    print quips[randint(0, len(quips)-1)]
    exit(1)


def central_corridor():
    print "The Gothons of Planet Percal #25 have invaded your ship and destroyed"
    print "your entire crew.  You are the last surviving member and your last"
    print "mission is to get the neutron destruct bomb from the Weapons Armory,"
    print "put it in the bridge, and blow the ship up after getting into an "
    print "escape pod."
    print "\n"
    print "You're running down the central corridor to the Weapons Armory when"
    print "a Gothon jumps out, red scaly skin, dark grimy teeth, and evil clown costume"
    print "flowing around his hate filled body.  He's blocking the door to the"
    print "Armory and about to pull a weapon to blast you."

    action = raw_input("> ")

    if action == "shoot!":
        print "Quick on the draw you yank out your blaster and fire it at the Gothon."
        print "His clown costume is flowing and moving around his body, which throws"
        print "off your aim.  Your laser hits his costume but misses him entirely.  This"
        print "completely ruins his brand new costume his mother bought him, which"
        print "makes him fly into an insane rage and blast you repeatedly in the face until"
        print "you are dead.  Then he eats you."
        return 'death'

    elif action == "dodge!":
        print "Like a world class boxer you dodge, weave, slip and slide right"
        print "as the Gothon's blaster cranks a laser past your head."
        print "In the middle of your artful dodge your foot slips and you"
        print "bang your head on the metal wall and pass out."
        print "You wake up shortly after only to die as the Gothon stomps on"
        print "your head and eats you."
        return 'death'

    elif action == "tell a joke":
        print "Lucky for you they made you learn Gothon insults in the academy."
        print "You tell the one Gothon joke you know:"
        print "Lbhe zbgure vf fb sng, jura fur fvgf nebhaq gur ubhfr, fur fvgf nebhaq gur ubhfr."
        print "The Gothon stops, tries not to laugh, then busts out laughing and can't move."
        print "While he's laughing you run up and shoot him square in the head"
        print "putting him down, then jump through the Weapon Armory door."
        return 'laser_weapon_armory'

    else:
        print "DOES NOT COMPUTE!"
        return 'central_corridor'

def laser_weapon_armory():
    print "You do a dive roll into the Weapon Armory, crouch and scan the room"
    print "for more Gothons that might be hiding.  It's dead quiet, too quiet."
    print "You stand up and run to the far side of the room and find the"
    print "neutron bomb in its container.  There's a keypad lock on the box"
    print "and you need the code to get the bomb out.  If you get the code"
    print "wrong 10 times then the lock closes forever and you can't"
    print "get the bomb.  The code is 3 digits."
    code = "%d%d%d" % (randint(1,9), randint(1,9), randint(1,9))
    guess = raw_input("[keypad]> ")
    guesses = 0

    while guess != code and guesses < 10:
        print "BZZZZEDDD!"
        guesses += 1
        guess = raw_input("[keypad]> ")

    if guess == code:
        print "The container clicks open and the seal breaks, letting gas out."
        print "You grab the neutron bomb and run as fast as you can to the"
        print "bridge where you must place it in the right spot."
        return 'the_bridge'
    else:
        print "The lock buzzes one last time and then you hear a sickening"
        print "melting sound as the mechanism is fused together."
        print "You decide to sit there, and finally the Gothons blow up the"
        print "ship from their ship and you die."
        return 'death'


def the_bridge():
    print "You burst onto the Bridge with the neutron destruct bomb"
    print "under your arm and surprise 5 Gothons who are trying to"
    print "take control of the ship.  Each of them has an even uglier"
    print "clown costume than the last.  They haven't pulled their"
    print "weapons out yet, as they see the active bomb under your"
    print "arm and don't want to set it off."
    
    action = raw_input("> ")

    if action == "throw the bomb":
        print "In a panic you throw the bomb at the group of Gothons"
        print "and make a leap for the door.  Right as you drop it a"
        print "Gothon shoots you right in the back killing you."
        print "As you die you see another Gothon frantically try to disarm"
        print "the bomb. You die knowing they will probably blow up when"
        print "it goes off."
        return 'death'

    elif action == "slowly place the bomb":
        print "You point your blaster at the bomb under your arm"
        print "and the Gothons put their hands up and start to sweat."
        print "You inch backward to the door, open it, and then carefully"
        print "place the bomb on the floor, pointing your blaster at it."
        print "You then jump back through the door, punch the close button"
        print "and blast the lock so the Gothons can't get out."
        print "Now that the bomb is placed you run to the escape pod to"
        print "get off this tin can."
        return 'escape_pod'
    else:
        print "DOES NOT COMPUTE!"
        return "the_bridge"

def escape_pod():
    print "You rush through the ship desperately trying to make it to"
    print "the escape pod before the whole ship explodes.  It seems like"
    print "hardly any Gothons are on the ship, so your run is clear of"
    print "interference.  You get to the chamber with the escape pods, and"
    print "now need to pick one to take.  Some of them could be damaged"
    print "but you don't have time to look.  There's 5 pods, which one"
    print "do you take?"

    good_pod = randint(1,5)
    guess = raw_input("[pod #]> ")


    if int(guess) != good_pod:
        print "You jump into pod %s and hit the eject button." % guess
        print "The pod escapes out into the void of space, then"
        print "implodes as the hull ruptures, crushing your body"
        print "into jam jelly."
        return 'death'
    else:
        print "You jump into pod %s and hit the eject button." % guess
        print "The pod easily slides out into space heading to"
        print "the planet below.  As it flies to the planet, you look"
        print "back and see your ship implode then explode like a"
        print "bright star, taking out the Gothon ship at the same"
        print "time.  You won!"
        exit(0)


ROOMS = {
    'death': death,
    'central_corridor': central_corridor,
    'laser_weapon_armory': laser_weapon_armory,
    'the_bridge': the_bridge,
    'escape_pod': escape_pod
}


def runner(map, start):
    next = start

    while True:
        room = map[next]
        print "\n--------"
        next = room()

runner(ROOMS, 'central_corridor')

It's a lot of code, but go through it, make sure it works, play it.

What You Should See

Here's me playing the game.

$ python ex41.py 

--------
The Gothons of Planet Percal #25 have invaded your ship and destroyed
your entire crew.  You are the last surviving member and your last
mission is to get the neutron destruct bomb from the Weapons Armory,
put it in the bridge, and blow the ship up after getting into an 
escape pod.


You're running down the central corridor to the Weapons Armory when
a Gothon jumps out, red scaly skin, dark grimy teeth, and evil clown costume
flowing around his hate filled body.  He's blocking the door to the
Armory and about to pull a weapon to blast you.
> dodge!
Like a world class boxer you dodge, weave, slip and slide right
as the Gothon's blaster cranks a laser past your head.
In the middle of your artful dodge your foot slips and you
bang your head on the metal wall and pass out.
You wake up shortly after only to die as the Gothon stomps on
your head and eats you.

--------
Such a luser.
learnpythehardway $ python ex/ex41.py 

--------
The Gothons of Planet Percal #25 have invaded your ship and destroyed
your entire crew.  You are the last surviving member and your last
mission is to get the neutron destruct bomb from the Weapons Armory,
put it in the bridge, and blow the ship up after getting into an 
escape pod.


You're running down the central corridor to the Weapons Armory when
a Gothon jumps out, red scaly skin, dark grimy teeth, and evil clown costume
flowing around his hate filled body.  He's blocking the door to the
Armory and about to pull a weapon to blast you.
> tell a joke
Lucky for you they made you learn Gothon insults in the academy.
You tell the one Gothon joke you know:
Lbhe zbgure vf fb sng, jura fur fvgf nebhaq gur ubhfr, fur fvgf nebhaq gur ubhfr.
The Gothon stops, tries not to laugh, then busts out laughing and can't move.
While he's laughing you run up and shoot him square in the head
putting him down, then jump through the Weapon Armory door.

--------
You do a dive roll into the Weapon Armory, crouch and scan the room
for more Gothons that might be hiding.  It's dead quiet, too quiet.
You stand up and run to the far side of the room and find the
neutron bomb in its container.  There's a keypad lock on the box
and you need the code to get the bomb out.  If you get the code
wrong 10 times then the lock closes forever and you can't
get the bomb.  The code is 3 digits.
[keypad]> 123 
BZZZZEDDD!
[keypad]> 234
BZZZZEDDD!
[keypad]> 345
BZZZZEDDD!
[keypad]> 456
BZZZZEDDD!
[keypad]> 567
BZZZZEDDD!
[keypad]> 678
BZZZZEDDD!
[keypad]> 789
BZZZZEDDD!
[keypad]> 384
BZZZZEDDD!
[keypad]> 764
BZZZZEDDD!
[keypad]> 354
BZZZZEDDD!
[keypad]> 263
The lock buzzes one last time and then you hear a sickening
melting sound as the mechanism is fused together.
You decide to sit there, and finally the Gothons blow up the
ship from their ship and you die.

--------
You died.  You kinda suck at this.

Extra Credit

1. Explain how returning the next room works.
2. Add cheat codes to the game so you can get past the more difficult rooms.
3. Instead of having each function print itself, learn about "doc string" style comments. Write the room description as doc comments, and change the runner to print them.
4. Once you have doc comments as the room description, do you need to have the function prompt even? Have the runner prompt the user, and pass that in to each function. Your functions should just be if-statements printing the result and returning the next room.
5. This is actually a small version of something called a "finite state machine". Read about them. They might not make sense but try anyway.
6. I have a bug in this code. Why is the door lock guessing 11 times?