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