rstdocs/examples/99bottles.py

   1 #!/usr/bin/env python
   2 #
   3 # :Copyright: 2007 Riccardo Murri, Guenter Milde.
   4 #             Released under the terms of the GNU General Public License
   5 #             (v. 2 or later)
   6
   7 # 99bottles.py
   8 # ============
   9 #
  10 # Print the famous `99 bottles of beer` song lyrics
  11 #
  12 # This is used as an introductory example to literate programming
  13 # in the `LiteratePrograms.org Wiki`_.
  14 #
  15 # The lyrics
  16 # ----------
  17 #
  18 # We take the lyrics from the Wikipedia_, which says in the
  19 # `99 bottles of beer`_ entry:
  20 #
  21 # The verse format is very formulaic, and can be expressed as follows:
  22 #
  23 # From 99 down to 1::
  24
  25 verse_template = """
  26 <number> bottles of beer on the wall
  27 <number> bottles of beer!
  28 Take one down, pass it around
  29 <number - 1> bottles of beer on the wall!"""
  30
  31 # There is much variation in the final verse. One common final verse (which
  32 # could potentially cause an infinite-loop motif) is::
  33
  34 final_verse = """
  35 No bottles of beer on the wall!
  36 No bottles of beer!
  37 Go to the store and buy some more
  38 99 bottles of beer on the wall!"""
  39
  40 # The Python program
  41 # ------------------
  42 #
  43 # There are a countless number of ways to implement a program that prints the
  44 # whole song in Python. The following examples uses a `for` loop and the
  45 # `replace` method of string objects.
  46 #
  47 # Basic version
  48 #
  49 # Count down from 99 to 1 and print the verses::
  50
  51 def print_verses_1(start_number=99):
  52     for number in xrange(start_number, 0, -1):
  53         verse = verse_template.replace("<number>", str(number))
  54         print verse.replace("<number - 1>", str(number-1 or "No"))
  55
  56 # Consider the singular case
  57 #
  58 # There is one problem left, we should check whether to print 'bottles' or
  59 # 'bottle'.
  60 #
  61 # An improved version will replace the "bottles" with a construct that
  62 # takes into account the actual number of bottles::
  63
  64 def print_verses_2(start_number=99):
  65     for number in xrange(start_number, 0, -1):
  66         verse = verse_template.replace("<number>", str(number))
  67         verse = verse.replace("bottles", "bottle" + plural_suffix(number))
  68         print verse.replace("<number - 1>", str(number-1 or "No"))
  69
  70 # where an auxiliary function returns the matching suffix (or not)::
  71
  72 def plural_suffix(number):
  73     if number != 1:
  74         return "s"
  75     else:
  76         return ""
  77
  78 # Still, the last line come out wrong, as here we have <number-1> bottles. To
  79 # treat this case we eiter could split the last line and treat it differently,
  80 # or use a modified template as e.g. ::
  81
  82 verse_template_2 = """
  83 <number> bottle<s> of beer on the wall
  84 <number> bottle<s> of beer!
  85 Take one down, pass it around
  86 <number - 1> bottle<s> of beer on the wall!"""
  87
  88 # together with::
  89
  90 def print_verses_3(start_number=99):
  91     for number in xrange(start_number, 0, -1):
  92         verse = verse_template_2.replace("<number>", str(number))
  93         verse = verse.replace("<s>", plural_suffix(number), 2)
  94         verse = verse.replace("<s>", plural_suffix(number-1), 1)
  95         print verse.replace("<number - 1>", str(number-1 or "No"))
  96
  97
  98 # Command line use
  99 # ----------------
 100 #
 101 # Print the lyrics if this script is called from the command line::
 102
 103 if __name__ == "__main__":
 104     print_verses_3()
 105     print final_verse
 106
 107
 108 # .. _Wikipedia: http://en.wikipedia.org
 109 # .. _99 bottles of beer: http://en.wikipedia.org/wiki/99_Bottles_of_Beer
 110 # .. _LiteratePrograms.org Wiki:
 111 #      http://en.literateprograms.org/LiteratePrograms:Welcome