CIS200 Lab Week 7 : global variables and sequential text files
---------------------------------------------------------

This material comes from Chapter 7 of the lecture notes
and Dawson's text.  Rather than lecture about it, we will cover it in lab.

A computer program can read a text (.txt) file
and write one.  We'll do some experiments to see this.


1. Writing a text file:  Do these experiments:

make a command window.  Then, do
> cd Desktop
> python
>>> myfile = open("test.txt", "w")
>>> myfile.write("this is line one\r\n")
>>> myfile.write("line two\r\n")
>>> myfile.close()

(This ``opens'' a new file to be written and then
writes two lines (strings) to it.  The  \r means ''return'' and
\n  means ``newline'' and are required to terminate a text line in a disk file.

The last command ``closes'' the file so that others may view it.)

Now, use  notepad  or some other editor to look at the file.


2. Reading a textfile: Do these experiments:

>python
>>> myfile = open("test.txt", "r")
>>> text = myfile.readline()
>>> text

(This should print  'this is line one\r\n'   Note the embedded  newline  character.
The point is,  readline  grabs _all_ the characters in the file
upto and including a newline character.)

Next, do this:

>>> text = text.strip()
>>> text

(this should print 'this is line one')

Next, do this:

>>> words = text.split(" ")
>>> words

(this should print,  ['this', 'is', 'line', 'one']  )

Finally, do this:
>>> text2 = myfile.readline()
>>> text2
>>> text3 = myfile.readline()
>>> text3

NOTICE THAT THE VALUE PRINTED FOR text3 IS THE EMPTY STRING, ''  !
When a file is completely read, any subsequent reads will return the
empty string.  This is how you know you have read the entire file !


NOW, FINISH THE LAB EXERCISE:

Download the  Words.py  module at 
  www.cis.ksu.edu/~schmidt/200s08/Assign
at the bottom of the page.  

Finish the module by writing the code for the   initialize and
nextWord   functions.  (Do  initialize  first,  then  nextWord.

You can test the functions with the test program,  TestWords.py
that is listed immediately after  Words.py  on the web page.