This is an indexing style used by scholars and which was once often available for some important books and some websites. The idea is the concordance permits you to read or see a word that has been indexed in its original context, as this can often aid the reader to decide whether or not the reference is indeed what they want or need.
The modules used are sys, regex and fileinput. The input can given through both stdin and through a file name.
I have designed the simillar program in C as well. It is impleted using linked-list and dynamic memory allocation, and further has no mermory leaks as of now.
There are some Testcases provided as well, designed by Dr. Zastre.