Homework Assignment 9

A Multi-File Search Program

CS 1510
Introduction to Computing
Fall Semester 2014

Due: Saturday, November 8, at 10:00 AM

Introduction

This assignment extends a program you wrote for Lab 8, grep. The focus of the assignment is to practice breaking a problem down into smaller pieces. You also will get to practice writing a function and working with files and strings.

Download this zip file. Its contents are explained in the next section.

Note the unusual due date.

Code for the Assignment

Use your solution for grep as a starting point. If your code is incomplete and incorrect, feel free to use my implementation of grep from Session 16 as your starting point.

You will also want to use two modules in your program:

• In Session 20, we built a function named multi_find(source, target, start, end) and added it to our str_utils module:

  Finds the positions of all occurrences of target in source that occur in the range start ≤ position < end. Returns a string containing zero or more indices, separated by commas.



• I gave written a function for you, named get_files() and put it in a module named homework09:

  Returns a collection of the names of all the text files in the current directory.

You can iterate over this collection using the same sort of for-loop we have used for strings and files:

     for filename in get_files():
         # suite of statements using filename

You can import these functions into your program by including these lines at the top of the file:

    from str_utils  import multi_find
    from homework09 import get_files

The zip file contains grep.py, str_utils.py, and homework09.py, along with several large text files you can use to test your program.

Spec 1: Multi-File Search

Write a program that

1. asks the user for a search string,
2. searches for the string in all the text files in the current directory, and
3. displays the number of matches in each file, along with each line that contains the search string.

For example, with the files in your test directory:

    >>> search for: er
    >>>

... will produce the following output.dat:

    *** File searched = dirda-excerpts.txt
    *** Total matches = 46
       4 Some people will never learn anything, for this reason,
       5 because they understand everything too soon.
    ...
     108 Ralph Waldo Emerson, Essays / Journals
     109 John Henry Newman, The Idea of a University


    *** File searched = hamlet.txt
    *** Total matches = 1970
      12 Dramatis Personae
      15 Marcellus, Officer.
    ...
    4458 Go, bid the soldiers shoot.
    4459 Exeunt marching; after the which a peal of ordnance

    *** File searched = macbeth.txt
    *** Total matches = 1124
       8 Dramatis Personae
      11 MACBETH, Thane of Glamis and Cawdor, a general in the King's army
    ...
    2842 Took off her life; this, and what needful else
    2844 We will perform in measure, time, and place.

    *** File searched = midsummer-nights-dream.txt
    *** Total matches = 1308
       2 A MIDSUMMER NIGHT'S DREAM
       8 DRAMATIS PERSONAE
    ...
    2398 Now to scape the serpent's tongue,
    2399 We will make amends ere long;

    *** File searched = test.txt
    *** Total matches = 10
      12 Dramatis Personae
      15 Marcellus, Officer.
    ...
      22 Rosencrantz, courtier.
      23 Guildenstern, courtier.

Notice that:

• The match is independent of upper- or lowercase, in either the search string or the string in the file.


• A single line may contain multiple matches. The number of matches reported is the total number of matches found in the file, not the number of lines matched.

Here is some design and programming advice:

• Create a function named search(filename, search_str) that does what the searching code in grep.py does. Have the function open and close the file to be searched. Test your function with the I/O code from grep.py.


• First, modify the function to use multi_find(). Then modify it to report the total number of matches.


• At first, print the total number of matches at the end of the output, rather than the top.


• At first, test your code with only one small text file, and write all output to the screen. Only after the main code works correctly should you try to write the output to a file and test against several files.


• Hint. The empty string '' evaluates to False when used in an expression that expects a boolean value.


• Hint. If you count the commas in a comma-separated string of numbers, you can find out how many numbers are in the string. The string method count() can help you.


• Remember to close each data file as soon as your program is finished using it.

Name your program search_files.py.

Demonstration of Correctness

Run the final version of your program using at least three different search strings with the text files in the zip directory. Make sure you choose strings that demonstrate the features of your program.

Make sure to copy your output.dat file before overwriting it with another run!

If You Don't Get Done. Turn in the latest version of your program that runs. Clearly document in your header block which features are implemented and which features are not implemented.

It is better to turn in incomplete code that works than code that doesn't work.

Deliverables

By the due date and time, submit:

• search_files.py
• output01.dat
• output02.dat
• output03.dat

Use the on-line submission system.

Make sure that your program meets the course programming standards.