A python script to let you read a book (e.g. a dictionary, an encyclopedia) in random order, keeping track of which pages have already been read.

bookmark.py

import sys,random

'''
USAGE
Let's say you want to read The Oxford Companion to Lulz, which has 819 pages. You would create a file with one line, "1:819", and save it as lulz.txt. Then you would run:

     python bookmark.py lulz.txt

This would return a random page that you haven't yet read. Let's say it was 42. You then read from 42 to 50. You record this fact by running:

     python bookmark.py lulz.txt 42 50

Which would alter lulz.txt to read:

     1:41
     51:819

That is to say, a listing of all the ranges of pages you haven't yet read.
Running the first command again would give you a random page in one of these ranges. Repeat until finished or bored.

'''

class R(object):
     def __init__(self, low, high=None):
          self.low = low
          if (high):
               self.high = high
          else:
               self.high = low
     
     def __sub__(b,a): # (B "minus" A)
          if (a == None):
               return b
          if (b == None):
               return None
          
          if ((b.high < a.low) or (a.high < b.low)):
               return b
          
          if (b.low == a.low):
               if (b.high <= a.high):
                    return None
               else:
                    return R(a.high+1,b.high)
          if (b.low < a.low):
               if (b.high <= a.high):
                    return R(b.low,a.low-1)
               else:
                    return [R(b.low,a.low-1),R(a.high+1,b.high)]
          if (b.low > a.low):
               if (b.high <= a.high):
                    return None
               else:
                    return R(a.high+1,b.high)

     def __str__(self):
               return str(self.low) + ":" + str(self.high)

### MAIN ###

filename = sys.argv[1]

unread = []

f = open(filename, 'r')
lines = f.readlines()
for line in lines:
    bounds = line.split(":")
    unread.append(R(
                    int(bounds[0]),
                    int(bounds[1])
                 ))
f.close()

if len(sys.argv) > 2: # I've read something, now I want to cross those pages off my list.

    low = int(sys.argv[2])
    if len(sys.argv) > 2:
        high = int(sys.argv[3])
    else:
         high = low

    justread = R(low,high)

    remaining = map(lambda x: x - justread, unread)

    flattened = []

    for item in remaining:
        if isinstance(item, list):
            for r in item:
                flattened.append(r)
        elif (item != None):
            flattened.append(item)

    f = open(filename,"w")

    for x in flattened:
        print x
        f.write(str(x) + "\n")

else: # Pick a page for me

    page_total = 0

    for r in unread:
        page_total += (r.high - r.low) + 1

    page = random.randrange(0,page_total+1)

    for r in unread:
        if ((page + r.low) <= r.high):
            print r.low + page
            print str(page_total) + " pages left in " + str(len(lines)) + " parts"
            break
        else:
            page -= (r.high - r.low) + 1