2.6 Itse1359-1240-the for loop

Table of contents

• Preface
  • What you have learned
  • What you will learn
  • Viewing tip
    • Figures
    • Listings
• General background information
• Discussion and sample code
  • Iterate on a sequence
  • The range function
• Visualize the programs
• Run the programs
• 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 have learned

In the most recent modules you learned about the while loop, operators , and the if statement. While studying that material, you learned some other things as well such as theconcepts of repetition, modularity, and decision logic.

What you will learn

You will learn about the for loop and the range function 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: most of the Figures and all of the 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 . Syntax of a for loop statement.
• Figure 2 . Output from the code in Listing 2.

Listings

• Listing 1 . Application of a for loop to a list and a string.
• Listing 2 . Using the range function to control a for loop.

General background information

You learned about the while loop in the earlier module titled Itse1359-1210-The while Loop . Although the syntax of the while loop in Python is different from the syntax of the while loop in other programming languages such as C, C++, C#, and Java, the behavior is very similar.

You learned about the if statement in the earlier module titled Itse1359-1230-The if Statement . Once again, although the syntax of the if statement in Python is different from the syntax of the if statement in the other programming languages listed above, the behavior is verysimilar.

That brings us to the for loop in Python. Neither the syntax nor the behavior of the Python for loop is similar to the syntax or the behavior of the primary for loop in those other languages.

However, some of those other languages have added a secondary for loop in recent years with behavior that is similar to the Python for loop. Also, the range function can be used with a Python for loop to produce behavior that is similar to the behavior of the primary for loops in those other languages.

Discussion and sample code

Iterate on a sequence

Python's for loop statement iterates over the items of any sequence (such as a list or a string) , in the order that they appear in the sequence. The syntax of a for loop is shown in Figure 1 .

The words " for " and " in " are keywords in the sequence. By that, I mean that they don't change from one script tothe next. The name of the variable var , the name of the sequence, and the statements are provided by the programmer and are subject to change from one script tothe next.