Added the flavour text and annotations to Robot Missile.

docs/books/computer-games/computer-battle-games/robot_missile/index.rst

@@ -2,10 +2,34 @@
 Robot Missile
 =============
 
+The year is 2582 and the people of Earth are in the midst of a battle against
+the Robots. A lethal Robot Missle has just landed and everyone is depending on
+you to find the secret code which unlocks its defuse mechanism. If you fail,
+the entire Earth Command Headquarters will be blown up.
+
+Your computer knows what the code letter is. You must type in your guess and
+it will tell you whether the code letter is earlier or later in the alphabet.
+You have four chances to find the correct letter before the missile blows up.
 
 The code
 ========
 
 .. literalinclude:: robot_missile.py
    :language: python
 
+Adding to the program
+---------------------
+
+You can make the computer print an extra message for a correct guess on the
+last go. Change line 37 to read::
+
+    print('You did it%s!' % (' (just)' if guesses == 4 else ''))
+
+This inserts some text between "it" and the exclamation mark; the text that is
+inserted is dependent on the value of `guesses` at the end of the loop.
+
+Puzzle corner
+-------------
+
+See if you can work out how to change the program to give you more or less
+changes of guessing the code letter.

docs/books/computer-games/computer-battle-games/robot_missile/robot_missile.py

@@ -1,3 +1,6 @@
+# Import `random` so we can generate random numbers.
+# The `string` module gives us access to string-related utilities,
+# like a list of lowercase characters.
 import random
 import string
 
@@ -7,26 +10,33 @@
 print('You have 4 chances.')
 print()
 
+# Choose, at random, a lowercase ascii character
 code = random.choice(string.ascii_lowercase)
 
+# Loop until we get a match, or we've tried 4 times
 guesses = 0
 success = False
 
 while not success and guesses < 4:
-    guess = input('What is your guess? ')
+    # Read a character from the user, and convert it to lower case
+    guess = input('What is your guess? ').lower()
     guesses += 1
 
-    if guess.lower() == code:
+    # Check to see if the guess is correct. If it is, flag the success;
+    # otherwise, print an error message hinting towards the final answer.
+    if guess == code:
         success = True
-    if guess < code:
+    elif guess < code:
         print('The code is later than %s in the alphabet' % guess)
-    if guess > code:
+    elif guess > code:
         print('The code is earlier than %s in the alphabet' % guess)
 
+# The loop has exited. Let the user know if they succeeded or not.
 if success:
-    print('TICK... FIZZ... CLICK...'
-          '\nYou did it!')
+    print('TICK... FIZZ... CLICK...')
+    print('You did it!')
 else:
-    print('BOOOOOOOOMMM...'
-          '\nYou blew it!'
-          '\nThe correct code was \'%s\'.' % code)
+    print('BOOOOOOOOMMM...')
+    print('You blew it!')
+    print()
+    print("The correct code was '%s'." % code)