There, I commented it. :)

scroller/char_sheet.py

@@ -1,3 +1,7 @@
+# Character Sheet object for holding the sprite sheet image file and additional
+# data such as character width and height.
+# This, of course, only takes into account fixed-width bitmap fonts.
+
 from pygame import image
 
 
@@ -8,6 +12,8 @@ class CharSheet:
         self.char_width = char_width
         self.char_height = char_height
 
+    # Retrieves the top-left x and y co-ordinates of a character on the sprite
+    # sheet.
     def get_sheet(self, character):
         index = self.characters.index(character.char)
 

scroller/character.py

@@ -1,3 +1,7 @@
+# Character object for managing an individual character and its attributes,
+# such as its location, speed and angle.
+
+
 class Character:
     def __init__(self,
                  x=0,

scroller/scroller.py

@@ -1,3 +1,6 @@
+# Scroller object within which the base text string is stored, and the current
+# list of visible characters is maintained and updated.
+
 from . import character
 
 
@@ -7,6 +10,7 @@ class Scroller:
         self.next_char = 0
         self.sheet_chars = []
 
+    # obtains the next character adds it to the list of characters to render.
     def get_next_char(self,
                       x=0,
                       y=0,
@@ -27,5 +31,7 @@ class Scroller:
         else:
             self.next_char = 0
 
+    # Removes a character from the render list, usually as a result of leaving
+    # the screen.
     def delete_first_char(self):
         self.sheet_chars.pop(0)

test.py

@@ -5,10 +5,18 @@ from scroller import char_sheet
 
 pygame.init()
 
+# For this example, I just wanted to work with a small 320x240 space.
+# Most of the old scrollers didn't have a lot of pixels to play with, after
+# all.
 size = width, height = 320, 240
 
 black = 0, 0, 0
 red = 255, 0, 0
+
+# A character list to match up the available ASCII characters with the
+# spritesheet. You could probably use ints instead. I used chars because I
+# forgot Python treat chars like strings. x_X
+
 characters = [' ', '!', '\"', '#', '$', '%',  '&', '\'', '(', ')', '*', '+',
               ',', '-', '.', '/', '0', '1', '2', '3', '4', '5', '6', '7', '8',
               '9', ':', ';', '<', '=', '>', '?', '@', 'A', 'B', 'C', 'D', 'E',
@@ -18,56 +26,83 @@ characters = [' ', '!', '\"', '#', '$', '%',  '&', '\'', '(', ')', '*', '+',
               'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y',
               'z', '{', '|', '}', '~', '©']
 
+# A CharSheet object holds the spritesheet and the character list, as well as
+# the dimensions of each sprite.
 char_sheet = char_sheet.CharSheet("jeromBD-metal-CCBY3.png",
                                   characters, 16, 16)
 
+# Placeholder co-ordinates just to centre the scroller while I built this.
 x = 320
 y = 120
 
+# We need a clock to restrain the framerate and not simply have the scroller
+# zipping across before the view even realises the program has started.
 clock = pygame.time.Clock()
 
+# Creates a new Scroller object, with the text we want to put into it.
+# Some space added to create a gap between repetitions.
 scroller = scroller.Scroller("IT'S BEEN... one week since you looked at me, " +
                              "cocked your head to the side and said \"I'm " +
                              "angry\"                         ")
 
+# Opens a pygame window to the previously-specified dimentions.
 screen = pygame.display.set_mode(size)
 
 while 1:
+
+    # Obtain a time delta that will be used to determine the full extent of the
+    # scroller's movement.
     dt = clock.tick(60)
 
+    # Blank the screen first. Don't want any trails (At least not in this case.
     screen.fill(black)
 
+    # Because for loops can't count themselves.
     i = 0
 
+    # If a character is not present on the scroller, create one.
+    # Else an exception will happen.
     if not scroller.sheet_chars:
         scroller.get_next_char(320, 120, 0.1, 2, 0, 20)
 
     for sheet_char in scroller.sheet_chars:
+        # Move each character to the left.
         sheet_char.x -= sheet_char.x_speed * dt
 
+        # Move the character up and down according to a sine wave.
         sheet_char.angle += sheet_char.y_speed
-
         sheet_char.y = ((sheet_char.radius *
                          math.sin(sheet_char.angle * math.pi / 180)) +
                         120)
 
+        # Delete the character from memory if has left the visible screen.
+        # i needs to be decreased too, as it has effectively stepped back one.
         if (sheet_char.x < -(char_sheet.char_width)):
             scroller.delete_first_char()
             i -= 1
         else:
+            # If the newest character has fully entered the visible screen,
+            # a new one can be introduced.
             if (i == (len(scroller.sheet_chars) - 1) and
                sheet_char.x <= (width - char_sheet.char_width)):
                 scroller.get_next_char(320, 120, 0.1, 2, 0, 20)
+
+                # This was just some debug stuff to figure out an issue.
                 print(str(len(scroller.sheet_chars) - 1) + " | " + str(i) +
                       " | " + str(scroller.next_char))
 
+            # All done, onto the next character, if there is one.
             i += 1
 
+        # Create a rect that will serve as a bounding box into which the
+        # character sprite will be drawn.
         sect = char_sheet.get_sheet(sheet_char)
         sprite = pygame.Rect((sect[0] * 16),
                              (sect[1] * 16), 16, 16)
 
+        # Draw the character to the screen.
         screen.blit(char_sheet.sheet, (sheet_char.x,
                     sheet_char.y), sprite)
 
+    # Bring the finished frame to the foreground.
     pygame.display.flip()