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

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P A R T I I I
P R O G R A M M I N G W I T H T H E R A S P B E R R Y P I
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
symbol:
# Example 2: A Python program from the ↵
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? ")