Example 2: Comments, Inputs, Variables And Loops - Raspberry Pi User Manual

158
R A S P B E R R Y P I
U S E R G U I D E
Example 2: Comments, Inputs,
Variables and Loops
Although the Hello World program is a useful, gentle introduction to a language, it's not ter-
ribly exciting . By its nature, it covers only the basics and fails to introduce some of the con-
cepts required for creating useful or interesting programs . The next example, however, uses
some of the basic tools required to make interactive programs in Python .
As in Example 1, begin by opening a new blank document in IDLE or your text editor, and
then start the program with the following shebang line:
#!/usr/bin/env python
As previously discussed, this line isn't strictly necessary unless the program is going to be
made executable, but it does no harm and is a good habit to develop .
Next, add a comment to the program to provide context if you need to open the file at a later
date . Note that this needs to be entered as a single line, as with all code lines that end in a
Æ symbol:
# Example 2: A Python program from the Æ
Raspberry Pi User Guide
In Python, anything following a hash symbol—with the exception of the shebang line—is
treated as a comment . When a comment is found, Python ignores it and skips to the next
line . Commenting your code is good practice: although you might know what a particular
section of code does now, things might not be so clear when you open the file again six
months down the line . Comments also help make code more maintainable, and if you decide
to share your code with other people, your comments help them understand what each sec-
tion is supposed to do . For simple programs, it's not strictly necessary to include com-
ments—but as with adding the shebang line, it's a very good habit to get in to . Comments
can be on their own line, as with the preceding comment, or at the end of a line, in which
case Python will run the code line up until it reaches the hash symbol .
Next, ask the user for his or her name using the following line:
userName = raw_input("What is your name? ")