Decisions Making Python
In the first half of this book, you mostly just printed out things called functions, but everything was basically in a straight line. Your scripts ran starting at the top and went to the bottom where they ended. If you made a function, you could run that function later, but it still didn’t have the kind of branching you need to really make decisions. Now that you have if, else, and elif, you can start to make scripts that decide things.
In the last script you wrote out a simple set of tests asking some questions. In this script you will ask the user questions and make decisions based on their answers. Write this script, and then play with it quite a lot to fi gure it out.
1 print "You enter a dark room with two doors. Do you go through door #1 or door #2?"
2
3 door = raw_input("> ")
4
5 if door == "1":
6 print "There's a giant bear here eating a cheese cake. What do you do?"
7 print "1. Take the cake."
8 print "2. Scream at the bear."
9
10 bear = raw_input("> ")
11
12 if bear == "1":
13 print "The bear eats your face off. Good job!"
14 elif bear == "2":
15 print "The bear eats your legs off. Good job!"
16 else:
17 print "Well, doing %s is probably better. Bear runs away." % bear
18
19 elif door == "2":
20 print "You stare into the endless abyss at Cthulhu's retina."
21 print "1. Blueberries."
22 print "2. Yellow jacket clothespins."
23 print "3. Understanding revolvers yelling melodies."
24
25 insanity = raw_input("> ")
26
27 if insanity == "1" or insanity == "2":
28 print "Your body survives powered by a mind of jello. Good job!"
29 else:
30 print "The insanity rots your eyes into a pool of muck. Good job!"
31
32 else:
33 print "You stumble around and fall on a knife and die. Good job!"
Output
You enter a dark room with two doors. Do you go through door #1 or door #2?
> 1
There's a giant bear here eating a cheese cake. What do you do?
1. Take the cake.
2. Scream at the bear.
> 2
The bear eats your legs off. Good job!
A key point here is that you are now putting the if- statements inside if- statements as code that can run. This is very powerful and can be used to create “nested” decisions, where one branch leads to another and another.
Study Drills
Make new parts of the game and change what decisions people can make. Expand the game out as much as you can before it gets ridiculous.
Can you replace elif with a sequence of if/else combinations?
You can in some situations, but it depends on how each if/else is written. It also means that Python will check every if/else combination, rather than just the first false ones, like it would with if/elif/else. Try to make some of these to figure out the differences.
How do I tell if a number is between a range of numbers?
You have two options: Use 0 < x < 10 or 1 <= x < 10, which is classic notation, or use x in range(1, 10).
