a simple concordance: read a text file from standard input, create a dictionary relating each word in the input text to a list of lines in which that word occurs. when running the program, supply a single parameter on the command line to print out all lines in the input text containing that word.

improved_concordance.py

import sys

concordance = dict()

for line in sys.stdin:
  line = line.strip()
  line_words = line.split(" ")
  for word in line_words:
    if word in concordance:
      concordance[word].append(line)
    else:
      concordance[word] = [line]

print concordance

search_word = sys.argv[1]

if search_word in concordance:
  print "\n".join(concordance[search_word])