sys module is
also where Python makes available the words typed on the command that
is used to start a Python script. These words are usually referred to
as command-line arguments and show up in
sys.argv, a built-in list of strings. C
programmers may notice its similarity to the C
argv array (an array of C strings). It's not
much to look at interactively, because no command-line arguments are
passed to start up Python in this mode:
To really see what arguments are about, we need to run a script
from the shell command line. Example 3-2
shows an unreasonably simple one that just prints the
argv list for inspection.
Example 3-2. PP3E\System\testargv.py
import sys print sys.argv
Running this script prints the command-line arguments list; note that the first item is always the name of the executed Python script file itself, no matter how the script was started (see the sidebar titled "Executable Scripts on Unix," later in this chapter).
python testargv.py['testargv.py'] C:\...\PP3E\System>
python testargv.py spam eggs cheese['testargv.py', 'spam', 'eggs', 'cheese'] C:\...\PP3E\System>
python testargv.py -i data.txt -o results.txt['testargv.py', '-i', 'data.txt', '-o', 'results.txt']
The last command here illustrates a common convention. Much like
function arguments, command-line options are sometimes passed by
position and sometimes by name using a "-name value" word pair. For
instance, the pair
-i option's ...