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The following two sample programs are used in an Python programming course that I teach. I find them useful in qualifying how to work with loops, couple loops, and queues. The first example uses two lists and coupled loops, while the second example uses a single dictionary and FILO queue approach.

The Twelve Days of Christmas lyrics can be printed like so with coupled loops:

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days = ['first','second','third','fourth'       \
       ,'fifth','sixth','seventh','eighth'      \
       ,'nineth','tenth','eleventh','twelveth']
 
verse = ['partridge in a pear tree.'     \
        ,'Two turtle doves,'             \
        ,'Three French hens,'            \
        ,'Four calling birds,'           \
        ,'Five gold rings,'              \
        ,'Six geese a-laying,'           \
        ,'Seven swans a-swimming,'       \
        ,'Eight maids a-milking,'        \
        ,'Nine ladies dancing,'          \
        ,'Tenth lords a-leaping,'        \
        ,'Eleven pipers piping,'         \
        ,'Twelve drummers drumming,']
 
# Loop forward, couple inner loop, and loop backward through list.
for i in range(0,len(days), 1):
  print("On the",str(days[i]),"day of Christmas my true love sent to me")
  for j in range(i, -1, -1):
    if (j > 0):
      print(" ",verse[j])
    elif (i == j):
      print("  A",verse[j])
    else:
      print("  and a",verse[j])

Recreating the problem into a single dictionary, you can solve by approaching it as a FILO queue. Here’s the approach:

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lyric = {'first':'partridge in a pear tree.'
        ,'second':'Two turtle doves,'
        ,'third':'Three French hens,'
        ,'fourth':'Four calling birds,'
        ,'fifth':'Five gold rings,'
        ,'sixth':'Six geese a-laying,'
        ,'seventh':'Seven swans a-swimming,'
        ,'eighth':'maids a-milking,'
        ,'nineth':'Nine ladies dancing,'
        ,'tenth':'Ten lords a-leaping,'
        ,'eleventh':'Eleven pipers piping,'
        ,'twelfth':'Twelve drummers drumming,'}
 
# Intiate a list for collecting stanza.
stanza = list()
 
# Generate a list of keys.
for i in lyric.keys():
  # Append keys to list of stanza.
  stanza.append(i)
 
  # Print the first line of each stanza.
  print("On the",i,"day of Christmas my true love sent to me")
 
  # Print the progressive stanza.
  for j in reversed(stanza):
    if (j not in ['first','twelveth']):
      print(" ",lyric[j])
    elif (i == j):
      print("  A",lyric[j])
    else:
      print("  and a",lyric[j])

As always, I hope this helps for approaches and solutions.

Written by maclochlainn

February 16th, 2020 at 12:42 am

Posted in Python,Python 3.x

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