4. Floating Little Leaves of Code

• 1. The Leaf as a Status Symbol in Ambrose
• 2. Small and Nearly Worthless
• 3. Chaining Delusions Together
• 4. The Miracle of Blocks

I’ve never seen the ham do anything but leak juice. Today, our business in Ambrose Caverns is with the elf. He is a crucial part of the next lessons. Let’s all make him feel welcome. Go start warming up your listening hats! (And please change out of those ridiculous stirrup pants.)

A prompt warning: this lesson is much slower. Stay with it. This will be a long, deep breath. The most crucial stage of your instruction. It may seem like you’re not learning much code at first. You will be learning concepts. By the end of this chapter, you will know Python’s beauty. The coziness of the code will become a down sleeping bag for your own solace.

1. The Leaf as a Status Symbol in Ambrose

Alright, Elf. Give us a quick rundown of the currency issues you’ve faced there in your kingdom.

Yeah, that’s not the way I remember it. This Elf was paging me constantly. When I refused to call him back, he somehow left a message on my pager. Meaning: it beeped a couple times and then printed out a small slip of paper. The slip said something to the effect of, “Get down here quick!” and also, “We’ve got to rid the earth of this scourge of entrepreneurial caterpillars, these twisted insect vikings are suffocating my blue crystals!”

Lately, the exchange rate has settled down between leaves and crystals. One tree-grown note is worth five crystals. So the basic money situation looks like this:

blue_crystal = 1
leaf_tender = 5

This example is, like, totally last chapter. Still. It’s a start. We’re setting two variables. The equals sign is used for assignment.

Now leaf_tender represents the number 5 (as in: five blue crystals.) This concept right here is half of Python. We’re defining. We’re creating. This is half of the work. Assignment is the most basic form of defining.

You can’t complain though, can you Elf? You’ve built an empire from cashing your blue crystals into the new free market among the forest creatures. (And even though he’s an elf to us, he’s a tall monster to them.)

Nonono. Hang on a sec. You’re not ready for what the Elf here is doing in his caves. You’ll think it’s all positively inhumane, naughty, sick, tweeested, yada yada.

Now You’re Going to Hear the Animal Perfect Mission Statement Because This Is A Book And We Have Time And No Rush, Right?

Back, back, way back before speedboats, I owned a prize race horse who took a stumble on the track. She did ten front flips and crashed into a guy who was carrying a full jar of mayonnaisse. We had blood and mayonnaisse up and down the track. Needless to say, she was a disaster.

The vet took one look at her and swore she’d never walk again. Her legs were gone and the vet wouldn’t allow a legless horse to just sit around. We’d need to put her down. He swore his life and career on it, insisting we divide into two parallel lines. The people who could not refute the doctor’s claims on one side; those too stubborn to accept his infallable medical reasoning on the other. The Elf, his pet ham, and I were the only ones in that second line.

So while the others heaped up trophies and great wreaths around the horse, bidding it a fond farewell before the bullet came to take him home, the Elf and I frantically pawed the Internet for answers. We took matter into our own hands, cauterizing her leg wounds with live crawdads. It worked great! We now had a horse again. Or at least: a horse body with a crustaceous abdominal frosting.

She scurried everywhere after that and lived for years in pleasantly moist underground cavities.

Animal Perfect is now the future of animal enhancement. They build new animals and salvage old-style animals for parts. Of course, they’ve come a long ways. When Animal Perfect started, you’d see a full-grown bear walk into Animal Perfect and you’d see a full-grown bear with sunglasses walk out. Completely cheesy.

Stick around and you’ll see a crab with his own jet pack. That’s a new 2024 model jetcrab.

But now, the whole operation is up and running. And the cleanliness of the place is astonishing. All the equipment is so shiny. Everything is in chrome. Oh, and all the staff have concealed weapons. They’re trained to kill anyone who enters unannounced. Or, if they run out of bullets, they’re trained to pistol whip anyone who enters unannounced.

Elf, make me a starmonkey.

Some imaginary Python for you:

pipe.catch_a_star()

Variable pipe. Method catch_a_star. A lot of Pythonists like to think of methods as a message. Whatever comes before the dot is handed the message. The above code tells the pipe to catch_a_star.

This is the second half of Python. Putting things in motion. These things you define and create in the first half start to act in the second half.

1. Defining things.
2. Putting those things into action.

So what if the star catching code works? Where does the star go?

captive_star = pipe.catch_a_star()

See, it’s up to you to collect the miserable, little star. If you don’t, it’ll simply vanish. Whenever you use a method, you’ll always be given something back. You can ignore it or use it.

If you can learn to use the answers that methods and operators give you back, then you will dominate.

Quickly then.

starmonkey = ratchet.attach( captive_monkey, captive_star )

The ratchet gets an attach message. What needs to be attached? The method arguments: the captive_monkey and the captive_star. We are given back a starmonkey, which we have decided to hang on to.

This is turning out to be such a short, little proggie that I’m just going to put it all together as one statement.

starmonkey = ratchet.attach( captive_monkey, pipe.catch_a_star() ) + deco_hand_frog

See how pipe.catch_a_star is right in the arguments for the method? The caught star will get passed right to the ratchet. No need to find a place to put it. Just let it go.

2. Small and Nearly Worthless

The hotel here in Ambrose is no good at all. The beds are all lumpy. The elevator is tiny. One guy put all his bags in the elevator and found out there wasn’t room for him. He hit the button and chased up the stairs after it all. But the stairwell turned out to be too narrow and his shoulders got wedged going up.

The soap mini-bars they give you are sized down for elves, so it’s impossible to work up a lather. I hate it. I keep mistaking them for contact lenses.

I turned on the faucet and nothing came out. Thing is: Ambrose is a place with magical properties, so I took a chance. I put my hands under the spigot. Invisible, warm wetness. I felt the hurried sensation of running water, darting through my fingers. When I took my hands away, they were dry and clean.

It was an amazing nothingness to experience. It was just like nil.

None

In Python, None represents an emptiness. It is without value. It isn’t zero. Zero is a number.

It’s Python’s own walking dead, a flatlined keyword. You can’t add to it, it doesn’t evolve. But it’s terribly popular. This skeleton’s smiling in all the pictures.

plastic_cup = None

The above plastic_cup is empty. You could argue that the plastic_cup contains something, a None. The None represents the emptiness, though, so go ahead and call it empty.

Some of you who have programmed before will be tempted to say the plastic_cup is undefined. How about let’s not. When you say a variable is undefined, you’re saying that Python simply has no recollection of the variable, it doesn’t know the var, it’s absolutely non-existent.

But Python is aware of the plastic_cup. Python can easily look in the plastic_cup. It’s empty, but not undefined.

False

The cat Trady Blix. Frozen in emptiness. Immaculate whiskers rigid. Placid eyes of lake. Tail of warm icicle. Sponsored by a Very Powerful Pause Button.

The darkness surrounding Blix can be called negative space. Hang on to that phrase. Let it suggest that the emptiness has a negative connotation. In a similar way, nil has a slightly sour note that it whistles.

Generally speaking, everything in Python has a positive charge to it. This spark flows through strings, numbers, regexps, all of it. Only two keywords wear a shady cloak: None and False draggin’ us down.

You can test that charge with an if keyword. It looks very much like the do blocks we saw in the last chapter, in that both end with an end.

if plastic_cup:
    print("Plastic cup is on the up 'n' up!")

If plastic_cup contains either None or False, you won’t see anything print to the screen. They’re not on the if guest list. So if isn’t going to run any of the code it’s protecting.

But None and False need not walk away in shame. They may be of questionable character, but if followed by not caters to the bedraggled. The if not keywords have a policy of only allowing those with a negative charge in. Who are: None and False.

if not plastic_cup:
  print("Plastic cup is on the down low.")

You can also use if and if not in a single line of code*, if that’s all that is being protected.

if plastic_cup: print "Yeah, plastic cup is up again!" 
if not plastic_cup: print "Hardly. It's down." 

And another nice trick: use and to add a variety of tests.

if plastic_cup and not glass_cup: print "We're using plastic 'cause we don't have glass." 

This trick is a gorgeous way of expressing, Do this only if a is true and b isn’t true.

Now that you’ve met False, I’m sure you can see what’s on next.

True

approaching_guy = True

I saw True at the hotel buffet tables today. I cannot stand that guy. His stance is way too wide. And you’ve never met anyone who planted his feet so hard in the ground. He wears this corny necklace made out of shells. His face exudes this brash confidence. (You can tell he’s exerting all of his restraint just to keep from bursting into Neo flight.)

To be honest, I can’t be around someone who always has to be right. This True` is always saying, “A-OK.” Flashing hang ten. And seriously, he loves that necklace. Wears it constantly.

As you’d suspect, he’s backstage at everything on the if event schedule.

if True: print("Hugo Boss") acts like print("Hugo Boss").

Occassionally, if will haul out the velvet ropes to exercise some crowd control. The double equals gives the appearance of a short link of ropes, right along the sides of a red carpet where only matches can be admitted.

if approaching_guy == True:
    print("That necklace is classic.")

The double equals is simply an ID check. Do the gentleman at both ends of this rope appear to match?

In this way, you control who if lets in. If you have a hard time getting along with True as I do, you can heartily welcome False.

if approaching_guy == False:
    print("Get in here, you conniving devil.")

Same goes for if not. The gateway is yours. Take possession of it.

Again, I Want You to Dominate

The double equals sign is a operator. Can you guess how it works?

approaching_guy == "Kevin"

It checks if the contents or data on both sides are an exact match, such as 5 == 5 or "Kevin" == "Kevin"

Now, do you remember what you need to do to dominate in Python? Use the answers the operators give you.

if approaching_guy == "Kevin":
  print("Kevin is here.")
end

In the above, how is the operator being used?

Let’s take the statement approaching_guy == "Kevin". This will pass every time approaching guy is set to "Kevin". Match. When it is set to "John" there’s no match, the double equals method answers with False. A shake of the head. That answer is given to if, who can’t accept a False. The print never sees realization.

Without an operator, if can still evaluate the truthiness of a variable. Here we check if at_hotel is truthy.

email = "why"
at_hotel = False
if at_hotel:
    email += "@hotelambrose.com"
else:
    email += "drnhowardcham.com"  # apprenticeship fallback email

Look at the above. What happens when at_hotel is True?

The if will return the answer given by the code it chooses to run. In the case of at_hotel being True, the first string, my e-mail address at Hotel Ambrose, will be returned. The else keyword marks code which will run, should if fail. If at_hotel is False, the if will answer with my e-mail address at Dr. N. Howard Cham’s office, where I take my apprenticeship.

Check the line of code inside the if. The plus equals += is the concatenation operator. To concatenate is to append, or add to the end.

Just as we saw with the =, the concatenator is a assignment operator. After adding to the end of the string, the concatenator also answers with that very string. So, the third line, which could be read as address _add to the end_ "drnhowardcham.com", gives back address, which is then assigned to the email.

Here’s a question: what if at_hotel is None in the above example? Which address is returned. None evaluates to False. So the else condition would be called and the email is set to "why@drnhowardcham.com".

Yes, nothing evaluates as False. By which I mean: None is falsey (evaluating to False). Just as 0 (integer), 0.0 (float), 0j (complex), and empty collections like "", [], or {}. Often None is a very useful case that we can test for.

if at_hotel == None:
    print("No clue if he's in the hotel.")
elif at_hotel == True:
    print("Definitely in.")
elif at_hotel == False:
    print("He's out.")
else:
    print("The system is on the freee-itz.")

You can see None here means we are not sure where he is. t_hotel == None is a comparison that ask “Are you None? Are you empty?”

If at_hotel is empty, Python doesn’t have any idea if I’m in the hotel or not. So if answers with the “No clue...” string. In order to handle the True or False possibilities, the elif keyword is used. While you can have only one if and one else, you can fill the in-between with an exorbitant number of elif keywords. Each elif acts as a further if test. Checking for a positive charge.

If you’re doing okay at this point, then you’re in tip-top shape for the rest of the book. You have seen some pretty tough code in the last few examples. You strong fellow.

3. Chaining Delusions Together

You finish reading the above comic and retire to your daybed for reflection. It’s one of those canopy affairs which is always logjammed with pillows. You sit atop the pile, gazing out upon the world. You see the tall smokestacks belching wide spools of fume and haze. The tangled concourses of freeways smattered with swift, shimmering traffic is but a gently pulsing eye muscle from your vantage point.

It is all so fantastic. How the colors of the horizon spread across the landscape as a great mix of butter and grease with a tablespoon of vanilla extract.

Yet, for all of the beauty which beckons for your attention, the images of the Elf and his Olympic Hopeful return. And more especially, that order for 55,000 starmonkeys. 55,000 starmonkeys, you think. Fifty-five Thousand.

You think of just the number itself. 55,000. It’s walking down a road. It might be in a forest, you don’t know for sure as your eyes are fixed right on the number itself. It’s stopping and talking to people. To tennis players, to a men’s choral group. There is merriment and good feeling. When it laughs, its lower zeros quiver with glee.

You want to talk to it. You want to skip along that forest trail with it. You want to climb aboard a jet bound to Brazil with it. And after five days and four nights at the leisureful Costa do Sauipe Marriott Resort & Spa, to marry it, to bear a family of 55,000 starmonkeys with it. To take possession of Nigeria with it.

With a flying leap, you dismount your pillow tower of isolation. Scrambling with the key, you unlock your roll top desk and pull out a sheet of paper, holding it firmly upon the desk. You begin scribbling.

Take possession of Nigeria with my new 55,000 starmonkeys... Over it, build Nigeria-sized vegetarians only casino and go-cart arena... Wings… we could have our own special sauce on the wings that’s different... Mustard + codeine = Smotchkkiss’ Starry Starmonkey Glow Sauce... Franchise, franchise… logos... Employee instructional videos... When you give the customer change, let them reach inside the frog on your hand to get it... If they have no change, at least put their reciept some place where they have to touch the frog... We’re leveling the playing field here... Advertise cheap pizza, let’s make our money off soda... Collect all 4 frosted glasses...

Wow, the ideas are really coming out. You literally had to smack yourself to stop. We need to put these in a safe place. Actually, we should store them on your computer and mangle the words. You look out the window and watch for FBI. I’m going to start this script.

The Flipping Script

print "Type and be ANGRY: "
angry_plans = input().upper()

Let this script be your confidante. It will ask for angry plans and make the first letter of each word upper case. The input functoin is built into Python like print. This method input will pause Python to let you type. When you hit Enter, input will then stop paying attention to your keyboard punchings and answer back to Python with a string that contains everything you typed.

The upper method is then used on the string that input is giving back. The upper method is part of the String class. Which means that anything which is a string has the upper method available. More on classes in the next chapter, for now just know that a lot of methods are only available with certain types of values.

I don’t think upper is going to cut it to get their attention. The authorities need to feel the “Angry Ranting” before the starmonkeys start can touch down in Lagos.

Maybe if we uppercase all letters in the string that will get their attention and add exclamation points at the end!!!

angry_plans = input().upper() + "!!!" # 3 exclamations means serious business

Now “Angry Ranting” becomes “ANGRY RANTING!!!”

Your Repetitiveness Pays Off

You hand me a legal pad, doused in illegible shorthand. Scanning over it, I start to notice patterns. That you seem to use the same set of words repeatedly in your musings. Words like starmonkey, Nigeria, firebomb. Some phrases even. Put the kibosh on. That gets said a lot.

Let us disguise these foul terms, my brother. Let us obscure them from itching eyes that cry to know our delicate schemes and to thwart us from having great pleasure and many go-carts. We will replace them with the most innocent language. New words with secret meaning.

I start up a word list, a Python Dictionary, which contains these oft seen and dangerous words of yours. In the Dictionary, each dangerous word is matched up against a code word (or phrase). The code word will be swapped in for the real word.

CODE_WORDS = {
  'starmonkeys' : 'Phil and Pete, those prickly chancellors of the New Reich',
  'catapult' : 'chucky go-go', 'firebomb' : 'Heat-Assisted Living',
  'Nigeria' : "Ny and Jerry's Dry Cleaning (with Donuts)",
  'Put the kibosh on' : 'Put the cable box on',
  'Hammer' : 'Technology'
}

The words which are placed before the arrow are called keys. The words after the arrows, the definitions, are often just called values.

Notice the double quotes around Ny and Jerry's Dry Cleaning (with Donuts). Since a single quote is being used as an apostrophe, we can’t use single quotes around the string. (Although, you can use single quotes if you put a backslash before the apostrophe such as: 'Ny and Jerry\'s Dry Cleaning (with Donuts)'.)

Should you need to look up a specific word, you can do so by using the square brackets method.

CODE_WORDS['catapult'] will answer with the string 'chucky go-go'.

Look at the square brackets as if they are a wooden pallet the word is sitting upon. A forklift could slide its prongs into each side of the pallet and bring it down from a shelf back in the warehouse. The word on the pallet is called the index. We are asking the forklift to find the index for us and bring back its corresponding value.

If you’ve never been to a warehouse, you could also look at the brackets as handles. Imagine an industrious worker putting on his work gloves and hefting the index back to your custody. If you’ve never used handles before, then I’m giving you about thirty seconds to find a handle and use it before I blow my lid.

Making the Swap

I went ahead and saved the Dictonary of code words to a file called wordlist.py.

from wordlist import CODE_WORDS

 # Get evil idea and swap in code words
idea = input("Enter your new idea: ")

for real, code in CODE_WORDS.items(): #loop over codes
    idea = idea.replace(real, code) 

 # Write the gibberish to a new file
idea_name = input("File encoded. Please enter a name for this idea: ").strip()
with open(f"idea-{idea_name}.txt", "w") as f: # Opens the file and automatically closes it when finished
    f.write(idea)

Script starts by pulling in our word list. Like gets and print, the import method is a built-in function, you can use it anywhere. It will look for a file named wordlist.rb and import CODE_WORDS.

After that, there are two sections. I am marking these sections with comments, the lines that start with pound symbols. Comments are useful notes that accompany your code. Folks who come wandering through your code will appreciate the help. When going through your own code after some time has passed, comments will help you get back into your mindset. And there’s software out there that can take your comments and build documents from them. (RDoc and Ri—see Expansion Pak #1!)

I like comments because I can skim a big pile of code and spot the highlights.

As the comments tell us, the first section asks you for your evil idea and swaps in the new code words. The second section saves the encoded idea into a new text file.

for real, code in CODE_WORDS.items(): #loop over codes
    idea = idea.replace(real, code) 

You see the for method? The for method is all over in Python. It’s available to use with Lists, Dictionaries, even Strings. Here, our CODE_WORDS dictionary is kept in a Dictionary. This for method will hurry through all the pairs of the Dictionary, one dangerous word matched with its code word, handing each coded pair to the replace method for the actual replacement.

In Python, replace is used to search and replace. Here, we want to find all the occurrences of a dangerous word and replace with its safe code word. With replace, you provide the word to find as the first argument, then the word to put in its place as the second argument.

Why do we have to asign the answer of replace method back to the idea?? Doesn’t replace already replace the text? You might think the line would read:

idea.replace( real, code ) Yes, with string methods we always need to hang on to its answer. When a method is done, we return a newly altered string. When you assign it to idea, you overwrite the old string.

Python strings cannot change. They are fixed. Python does not have a change-in-place string methods. Instead, both normal string replacement and any new string method returns a fresh string, leaving the old string alone. (Python stays calm and quiet, never destroying your personal property.)

Text Files of a Madman

Let us now save the encoded idea to a file. (Oh, I forgot we are still doing this spy stuff.)

# Write the gibberish to a new file
idea_name = input("File encoded. Please enter a name for this idea: ").strip()
with open(f"idea-{idea_name}.txt", "w") as f: # Opens the file and automatically closes it when finished
    f.write(idea)

This section starts by asking you for a name by which the idea can be called. This name is used to build a file name when we save the idea.

The strip method is for Strings. This method trims spaces and blank lines from the beginning and end of the string. This will remove the Enter at the end of the string you typed. But it’ll also handle extra spaces if you accidentally left any.

After we have the idea’s name, we open a new, blank text file. The file name is built by adding strings together. If you typed in 'mustard-plus-codeine', then our math will be: 'idea-' + 'mustard-plus-codeine' + '.txt'. Python presses these into a single string. 'idea-mustard-plus-codeine.txt' is the file.

We’re using the function open to open up the file object stream. Up until now, we’ve used several built-in functions to do our work. We hand the print method a string and it prints the string on your screen. One secret about built-in functions like print: they are all stored inside a hidden module called builtins. You can call them explicitly by writing builtins.print() instead of just print().

builtins.print( "55,000 Starmonkey Salute!" )

What does this mean? Why does it matter? It means builtins is the center of Python’s universe. Wherever you are in your script, builtins is right beside you. You don’t even need to spell builtins out for Python. Python knows to check builtins.

Most methods are more specialized than print or input. Take the open for example. The creator of Python, the handsome Guido van Rossum, gave us various methods for a opened file object to read, write, or close files since the first version of Python ever created.

• content = file.read() will read the entire file and will answer back with a string containing all of the text from your idea .
• f.write(idea) will write to the end of the file.
• f.close() will close the file.

These file object methods are all built right into Python. They are all part of the io module, core tools for working with streams of data. So, while you can safely call builtins methods without needing to type builtins, Python doesn’t automatically check the file object methods. You’ll need to open a strem and get a file object first to use any of the methods.

idea_name = input("File encoded. Please enter a name for sassy ideas file: ").strip()
with open( 'sassy_ideas-' + idea_name + '.txt', 'w') as f: # Opens the file and automatically closes it when finished
    f.write(idea)
# File automatically closes here

We pass two arguments into open. The first is the file name to open. The second is a string containing our file mode. We use 'w', which means to write to a brand-new file. (come file mode options are: 'w' to write, 'r' to read from the file, 'a' to add to the end of the file.)

The file is opened for writing and we are handed back the file in variable f, which can be seen sliding down the chute into our with Context Managers. Inside the context manager, we write to the file. When the context manager finishes, our file is closed as well automatically.

Settle Down, Your Ideas Aren’t Trapped

Here, let’s get your ideas back to their original verbage, so you can ruminate over their brilliance.

from glob import glob
# Assuming CODE_WORDS is defined in a separate wordlist.py file
from wordlist import CODE_WORDS

# Print each idea out with the words fixed
for file_name in glob("idea-*.txt"):
    with open(file_name, "r", encoding="utf-8") as f:
        idea = f.read()

    for code, real in CODE_WORDS.items(): #decoding the encoded message
        idea = idea.replace(code, real)

    print(idea)

By now, you should be up to snuff with most of this example. I won’t bore you with all of the mundane details. See if you can figure out how it works on your own.

We have an interesting class method here, though. The glob method searches a directory (some of you may call them “folders”). The glob method copies from Unix command with the same name to search for files. When you think of glob, think of a globe and spinning a spherical map to search the whole folder for your files. (Can you start to see the shiny, glinting gorgeousness of Python?)

So we’re using the spinning globe to get those files in the directory which match 'idea-*.txt'. The glob method will use the asterisk as a wildcard. We’re basically saying, “Match anything that starts with idea- and ends with .txt.” The spinning globe spins off to the directory and comes back with a list of all matching files.

That list of files will come in the form of List the Caterpillar, with a String for each file. If you are curious and want to play with glob, try this:

from glob import glob
# 1. Get all files and folders in the current directory
print(glob.glob('*'))

# 2. Get all .txt files in a specific folder
print(glob.glob('documents/*.txt')

4. The Miracle of Blocks

Since you and I are becoming closer friends as we share this time together, I should probably let you in on a bit of the history going on here. It’s a good time for a break I say.

First, you should know that Blix is my cat. My second pet to Bigelow. Granted, we hardly see each other anymore. He’s completely self-sufficient. I’m not exactly sure where he’s living these days, but he no longer lives in the antechamber to my quarters. He emptied his savings account about seven months ago.

He does have a set of keys for the house and the Seville. Should he ever find himself stranded, I will gladly step away from our differences and entertain his antics around the house again.

Make no mistake. I miss having him around. Can’t imagine he misses my company, but I miss his.

A Siren and A Prayer

I first saw Blix on television when I was a boy. He had a starring role on a very gritty police drama called A Siren and A Prayer. The show was about a god-fearing police squad that did their jobs, did them well, and saw their share of miracles out on the beat. I mean the officers on this show were great guys, very religious, practically clergy. But, you know, even clergymen don’t have the good sense to kill a guy after he’s gone too far. These guys knew where to draw that line. They walked that line every day.

So, it was a pretty bloody show, but they always had a good moral at the end. Most times the moral was something along the lines of, “Wow, we got out of that one quick.” But there’s serious camaraderie in a statement like that.

The show basically revolved around this one officer. “Mad” Dick Robinson. People called him Mad because he was basically insane. I can’t remember if he was actually clinically insane, but people were always questioning his decisions. Mad often blew his top and chewed out some of the other officers, most of whom had unquestionable moral character. But we all know it’s a tough world, the stakes are high out there, and everyone who watched the show held Mad in great regard. I think everyone on the squad grew quite a bit as people, thanks to Mad’s passion.

The officers couldn’t do it all themselves though. In every single episode, they plead with a greater force for assistance. And, in every single episode, they got their tips from a cat named Terry (played by my cat Blix.) He was just a kitten at the time and, as a young boy tuning into A Siren and A Prayer, I found myself longing for my own crime-sniffing cat. Terry took these guys down the subway tunnels, through the rotting stench of abandoned marinas, into backdoors of tall, industrial smokestacks.

Sometimes he was all over an episode, darting in and out, preparing traps and directing traffic. But other times you wouldn’t see him the whole episode. Then you’d rewind through the whole show and look and look and look. You’d give up. He can’t be in that episode.

Still, you can’t bear to let it go, so you go comb through the whole episode with the jog on your remote, combing, pouring over each scene. And there he is. Way up behind the floodlight that was turned up too high. The one that left Mad with permanent eye damage. Why? Why burn out the retinas of your own colleague, Terry?

But the question never got answered because the series was cancelled. They started to do special effects with the cat and it all fell apart. In the last episode of the show, there is a moment where Terry is trapped at the top of a crane, about to fall into the searing slag in the furnace of an iron smelt. He looks back. No going back. He looks down. Paws over eyes (no joke!), he leaps from the crane and, mid-flight, snags a rope and swings to safety, coming down on a soft antelope hide that one of the workers had presumably been tanning that afternoon.

People switched off the television set the very moment the scene aired. They tried changing the name. First it was God Gave Us a Squad. Kiss of Pain. Then, Kiss of Pain in Maine, since the entire precinct ended up relocating there. But the magic was gone. I went back to summer school that year to make up some classes and all the kids had pretty much moved on to football pencils.

Lambda

A couple years ago, I started teaching Blix about Python. When we got to this part this part of the lessons, he said to me, “Lambda functions remind me of Mad Dick Robinson who was always good with the ladies.”

“Oh?” I hadn’t heard that name in a while. “I can’t see how that could be.”

“Well, people say lambda functions can be difficult to understand.”

“They’re not difficult,” I said. “A lambda function is just temparory code grouped together without having to give it a name. Just like a function, with lambda we have arguments that are passed in and the function code or expression that gets evaluated. Just like a function, we use a colon to separate the two."

Blix shook his head not understanding.

"For lambda x: x.lower(), we could read it as take x and give back lowercase x. You try to read this function." "

`(lambda x: x * 2)(4)`  # return 8

"Umm. take x and give back x times 2. Seems dumber than Mad Dick Robinsons."

"Exactly. Why not just write 4*2? Well Lambda is useful as short cut when we want to multiple numbers by two many times."

times_by_two = lambda x: x * 2
times_by_two(1) # gives 2
times_by_two(4) # gives 8
times_by_two(2) # gives 4
times_by_two(8) # gives 16

"That seems awfully...silly? Why not just use multiplication and a list comprehension?" said Blix, remembering the assembly line from Chapter 3.

"You mean like this? [n*2 for n in [1,4,2,8]]?"

"Ah yes! That seems like a less dumb way to double a bunch of numbers."

"Yes, but back on topic. The power of the **lambda function ** comes when you just want to make a quick one-off calculation. It works sort of like a disposable function, that you use once and never use again.”

"Like a one night stand?" asked Blix.

"Well, I guess you could think of it like that but..."

"Oh great! I have a perfect use case then. Write me a lambda function to help expedite my dating! I have a long list of profiles. Can you help me narrow them down to ones open to.. you know..."

"What?"

"You know..."

"Cheap flings? I don't think Python was meant for that..."

"Just make with the code already!"

profiles.py

profiles = [
    "Looking for something casual, fun dates, and picnics and lasagna.", 
    "I'm looking for marriage and a litter of kittens. Only serious cats please.", 
    "I'll be visiting the neighborhood so short-term works great!", 
    "I am looking for Mr. Purfect. He needs to have all his shots."
]

import profiles
# Define the lambda function rule
is_open_to_hookups = lambda bio: "casual" in bio or "short-term" in bio

# Test profiles for tags by runing the lambda function and print the results
results = filter(is_open_to_hookups, profiles)
print(list(results))

"Ah! Hmm. lambda bio: and filter? What's that...? Well, I don't really care. Did I get any matches?"

"Blix, try to understand the code first. The lambda function takes in an argument bio and checks if the words casual or short-term are in the bios. We then apply this to your list of potential suitors or suitresses using filter to filter and return the matches, and voilà, we get a list of... eligible mates."

"I see, I see... This will really amp up my dating life!" said Blix pressing the pads of his fingers together, lost in deep thought.

"That's the first time I think I've heard Python helping someone getting laid."

“No getting back to Mad Dick Robinsons. Mad was just an officer, sworn to uphold his duty,” I said. “But he was a real miracle to watch out in the field. Now, this example shows pick up line from the show that Mad Dick used to get dates" I pointed to an example I’d written down for him using lambda.

loud_pickup_line = (lambda x: x.upper()+"!!!")("You look like you could use help to steer your car. Come sit on my lap and I'll teach you.")

“I get it, apply upper to each item it comes across and + "!!!" adds exclamation marks. So the lambda works like some sort of placeholder function?” he said.

I nodded yes.

“I understand, sort of, but your examples are too weird. Could you give an example that's related to my life? What about my cat toys?" he said pointing a paw at the dirty sock and toy mouse across the room.

"That's my sock, not your toy..." I tried to argue but gave up mid-sentence.

I scribled an example on the page.

kitty_toys = 
    [{"name": "sock", "fabric": "cashmere"}] +
    [{"name": "mouse", "fabric": "calico"}] +
    [{"name": "eggroll", "fabric": "chenille"}]

#get the fabrics
fabrics = list(map(**lambda toy: toy["fabric"]**, kitty_toys))

“This is a small miracle,” he said. “I can’t deny its beauty. Look, there are my kitty_toys_, laid out with their characteristics. Behold, the lambda function, grabbing each fabrics using ap.”

“I apologize if your list of toys looks a bit confusing,” I said. Like you, Blix had learned about the List, the caterpillar stapled into the code, with square brackets on each side and each item separated by commas. (Ah, here is one: [1, 2, 3].) He had also been taught the Dictionary, with curly braces on each end which look like small, open books with words in the dictionary matched up with its definition by an colon. (Be beholden: {'blix': 'cat', 'why' : 'human'}.)

“Yes, vexing,” he said. “It has square brackets like it’s an List, but inside colons like it’s a Dictionary. I don’t think you’re going to get away with that.”

“It does seem a bit odd, doesn’t it?” I said, tease-nudging him with a spoon. “I’ve done your kitty toy list in a mix of the two. I’m using a shortcut. Which is: A bunch of Lists each with a single Dictionary inside it.“

“Oh, I see,” he said. “You criss-crossed ‘em. How neat!”

“Yes, yes, you’re on it,” I said. He was also very good with a protractor. “I have three Lists, each with a Dictionary inside. Notice the plus signs? I’m adding them into one big List."

"Here’s another way of writing it…” I jotted down.

kitty_toys = [
    {"name": "sock", "fabric": "cashmere"}, 
    {"name": "mouse", "fabric": "calico"},
    {"name": "eggroll", "fabric": "chenille"}
    ]

One List, which acts as our list of chew toys. Three Dictionaries in the List to describe each toy. The first toy is described as {"name": "sock", "fabric": "cashmere"}, the second {"name": "mouse", "fabric": "calico"} and so on. A List of Dictionaries!

Sorting and Iterating to Save Lives

“Let’s sort your toys by name now,” I said. “Then, we’ll print them out in that order.”

sorted_toys = sorted(kitty_toys, key=lambda toy: toy["name"])

“How does sort_by work?” asked Blix. “I can tell it’s a built-in function you can use with List. Because kitty_toys is an List. But what is key and why do we need to use lambda again!?”

“Okay, key is telling sorted how we want to sort our list. Each dictionary element has a name and a fabric. We have to tell Python, which of these to use in our sorting."

"But why does it say key=. I haven't seen that before."

Python uses position most of the time for function arguments. For example in def greet_user(name, age): the first argument is name and the second is age. But Python sometimes uses what is called keyword (named) arguments to improve code readability. These methods intercept outside assignment to instance variables and we'll talk more about them in Chapter 5. In the mean time, just think of key= as a new way to pass in an argument to the sorted function.

"OH!! Soo sort by name then. The key is what we sort by! It make sense to sort by name, so my eggroll goes to the top of the list."

"Right, the key is defined as lambda toy: toy["name"] so we sort by the toy's name."

"That lambda function again? I thought we were done with that?" Blix replied with a grimace.

"Yes, but it's not so complicated. We'll split that lambda function into its two sides, arguments and expression. Do you see toy is the lambda argument,” I said. “And toy["name"] is the resulting expression we will return to sort by.”

Ah okay sure, toy["name"]. Right, a Dictionary look up. And sorted??”

“The sorted function takes a key as the second argument, Blix. It cycles, through a list of things and sorts each item based on what that function returns."

Blix nodded looking at the eggroll.

"You remember that episode when Mad…”

“Episode?” he said. Yeah, he can’t understand the concept of TV dramas. Yeah, I’ve tried explaining.

“Or, yeah, remember that one eyewitness account we watched where Mad was trying to talk down that crazy spelling bee contestant from the ledge of an college library?”

“I remember it better than you because I was riding in a remote control plane.” Yep, it was one of those episodes.

“Do you remember how Mad got the guy to come down?” I asked.

“People in spelling bees love letters,” said Blix. “So what Mad did was a genius move on his part. He started with the letter A and gave reasons, for all the letters of the alphabet, why the guy should walk back down the building and be safe on the ground.”

”’A is for the Architecture of buildings like this,’” I said, in a gruff Mad voice. ”’Which give us hope in a crumbling world.’”

”’B is for Big Guys, like your friend Mad the Cop,’” said Blix. ”’Guys who help people all the time and don’t know how to spell too great, but still help guys who spell really great.’”

“See, he went through all the letters, one at a time. He was iterating through them.” It Err Ate Ing.

“But the guy jumped anyway, Why. He jumped off on letter Q or something.”

”’Q is for Quiet Moments that help us calm down and think about all of life’s little pleasures, so we don’t get all uptight and starting goofing around on tiptoes at the very edge of a big, bad building.’”

“And then he jumped,” said Blix. He shook his head. “You can’t blame Mad. He did his best.”

“He had a big heart, that’s for sure,” I said, patting Blix on the shoulder.

sorted_toys = sorted(kitty_toys, key=lambda toy: toy["name"])
for toy in sorted_toys:
    print(f"Blixy has a {toy['name']} made of {toy['fabric']}")

“As for your sorted, it starts at the top of the list and goes through each item, one at a time. So toy is one of those items. With each item, sorted stops and looks up the name in the dictionary, finds the toy name, and then lets you figure out what to do with it.”

“Okay, so toy takes turns being each of the different toys I have.”

“That’s right,” I said. “You know how I’ve really been harping on using the answers that functions give you? Here, we’re simply looking up the toy’s name. The lambda then answers to sorted function's key argument with the name string, such as "mouse" or "sock".

Once it’s done cycling through the whole list,sorted will have alphabetically compared each of the names strings and will give back a new sorted List of toys!”

An Unfinished Lesson

“That’s good enough for today,” said Blix. “Can I have a fresh saucer of milk, please?”

I filled his saucer to the brim and he guzzled from it for some time while I took a poker and jabbed at coals in the fireplace. My mind wandered and I couldn’t help but think further of lambda. I wondered what I would teach Blix next.

I probably would have taught him about continue. When you are iterating through a list, you may use continue to skip on to the next item. Here we’re counting toys that have a non-eggroll shape by skipping those that do with continue.

non_eggroll = 0
for toy in kitty_toys:
    if toy['shape'] == 'eggroll':
        continue
    non_eggroll = non_eggroll + 1

I could also have taught him about break, which kicks you out of an iterating loop. In the code below, we’ll print out each of the toy dictionaries until we hit the toy whose fabric is lyrca. The break will cause the loop to abruptly end.

for toy in kitty_toys:
    if toy['fabric'] == 'lyrca':
        break
    print(toy)

I never got to teach him such things. I continued poking away at a particularly stubborn coal which was caught in the iron curtain of the fireplace and threatened to drop on my antelope skin rug.

As I hacked away ferociously at the black stone, Blix slipped away, presumably on the bus bound for Wixl, the very bustling metropolis of the animal economies. Who knows, he may have first stopped in Ambrose or Riathna or any of the other villages along the way. My instinct say that Wixl was his definitely his final stop.

Without any student to instruct and coax along, I found myself quite lonely, holed up in the estate. In the stillness of the dead corridors, I began to sketch out a biography in the form of this guide.

I worked on it whenever I found myself bored. And when I wasn’t bored, I could always switch on The Phantom Menace to get me in the mood.