1.11 Itse1359-1060-syntax  (Page 7/4)

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• Introduction
• Program construction
  • A physical line
  • A logical line
    • Statements and logical lines
    • Comments
  • Explicit line joining
    • The backslash character
    • For illustration only
    • No spaces or comments allowed
    • Otherwise illegal
  • Implicit line joining
  • Blank lines
• Indentation
  • Indentation is used to determine grouping of statements
    • A blessing and a curse
    • No safety nets
  • An example of correct indentation
    • Compare A with B and take appropriate action
    • A compound statement
    • Group behavior
    • Another sample script
    • Members of the group
    • An opinion
    • Indentation details
      • Leading whitespace
      • Tabs
  • The bottom line on indentation
• 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. It explains some of the mechanics of putting together aPython program.

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.)

Figures

• Figure 1 . Two physical lines.
• Figure 2 . Output from the script in Listing 4.

Listings

• Listing 1 . Explicit line joining.
• Listing 2 . Implicit line joining.
• Listing 3 . Blank lines and whitespace.
• Listing 4 . An example of correct indentation.
• Listing 5 . Another sample script.

Introduction

You have learned how to write some simple programs and how to execute them interactively.

You have also learned how to capture simple programs in script files and how to execute those script files.

Now it is time to learn a little more about the mechanics of putting together a Python program.

Program construction

Conceptually, programs are constructed from statements, and statements are composed of expressions. In practice, you need to know how to constructstatements from a physical viewpoint.

A Python program is divided into a number of logical lines . A logical line is constructed from one or more physical lines.

A physical line

A physical line ends with the character or characters used by your platform for terminating lines.

On Unix, this is the linefeed character. On Windows, it is the carriage return character followed by the linefeed character. On Macintosh, it is the carriage return character.

We refer to this in programming jargon as the newline character (even though it is actually two characters on Windows systems) .

Basically, a physical line is what you get when you type some characters into your text editor and press the Enter key, the Return key, or whatever you call that key on your keyboard. (Actually you don't even need to type characters before pressing the Enter key, in which case you get a blankline.)