Section 1: Persistent Data

 Table of Contents > Chapter 6 > Section 1 

To this point, data that has been produced by our programs is not persistent.  In other words, it does not exist beyond the time frame in which our program or Python shell is running.  If we want to use it at some later time, we must make a note of it by manually copying the values to a piece of paper or to a file.  If the amount of data that we want to persist is small, this is not hard to do but this approach is not practical when a large amount of data is involved.

When working with spreadsheets, word processors and graphics programs, for example, we are used to having to save our work to a file before we exit the program.  When we save work to (or write data to) a file, we are ensuring that the data that we have produced with the program persists after that program has terminated.  At a later time, we can continue to work with the data by loading it (or reading it in) from the file in which it is stored.

In this section of the course we look at how to read and write data to files.  Files can be broken down into two broad categories: text files and binary files.  Text files used to store raw textual data are such that certain characters in the file are interpreted in particular ways.  For example, \n is interpreted (on some systems) as an end-of-line.  So, rather than displaying \n on the screen, we see a line break.  Binary files, on the other hand, are used to store image data, audio data and other data.  In this course, we will consider the use of text files only.