Itse1359-1510-reading and writing text files

Table of contents

• Preface
  • What you will learn
  • Viewing tip
    • Figures
    • Listings
• General background information
• Discussion and sample code
  • Open a text file for writing
  • Write text and close the file
  • Read and print the file contents with a for loop
  • Append more text to the file
  • Read and print the file contents with a while loop
• Run the program
• Complete program listing
• Miscellaneous

Preface

This module is one in a collection of modules on Python designed for teaching ITSE 1359 Introduction to Scripting Languages: Python at Austin Community College in Austin, TX.

What you will learn

You will learn how to read, write, and append to text files using Python in this module.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand the Listings while you are reading about them.

(Note to blind and visually impaired students: all of the Figures and Listings inthis module are presented in plain text format and should be accessible using an audio screen reader or a braille display. Note however that the requiredindentation may not be properly represented by an audio screen reader.)

Figures

• Figure 1 . Output from the code in Listing 3.
• Figure 2 . Output from the code in Listing 5.
• Figure 3 . Output produced by the code in Listing 6.

Listings

• Listing 1 . Open a text file for writing.
• Listing 2 . Write text and close the file.
• Listing 3 . Read and print the file contents with a for loop.
• Listing 4 . Append more text to the file.
• Listing 5 . Read and print the file contents with a while loop.
• Listing 6 . Complete program listing.

General background information

From time to time you may need to read, write, or append to files. I will present and explain a relatively simple program in this module that will get youstarted down that path. However, this module is not intended to be a comprehensive tutorial on file i/o. Instead, I will refer you to other onlineresources for more information if and when you need it. The following web sites provide important information in this regard:

• tutorialspoint -- Python Files I/O
• The Python Tutorial -- Reading and Writing Files
• Python Library Reference (version 2.3)

Discussion and sample code

The program that I will present and explain in this module begins by writing a text file named "SampleTextFile.txt" into the current directory and populating it with five lines of text. If a file already exist havingthat name in the current directory, it will be overwritten by the new file.

Then the program uses a for loop as an iterator to read and print each line of text from the file.

After that, the program appends two additional lines of text to the file and uses a while loop to read and print the seven lines of text from the file.

A complete listing of the program is provided in Listing 6 . The output from the program is shown in Figure 3 . As usual, I will break the program down and explain it in fragments. The first fragment is shown in Listing 1 .