Commands starting with "%" and "-" characters
Question: I've seen these in books and over the internet but never understood them.
Something like this

    
    
    ...modify changer.py without stopping Python...
    % vi changer.py
    

and

    
    
    python -mtimeit -s
    

What do they mean? And where are they applied?


Answer: `%` is the C shell prompt. It's not universal for all shells. Depending on
what kind of shell you're using, you could get a different kind of prompt when
its waiting for your commands. For example UNIX shells commonly use the `$`
sign and the Windows CMD prompt uses the current directory followed by a `>`
character.

`vi` is simply a _shell command_ which calls vi, a Unix-platform text editor.
In your example, he's just using the text-editor vi to modify the Python
script changer.py. It has nothing to do with Python other than the fact that
the text editor can be used to edit Python scripts.

`python -mtimeit -s` is using the `-m` _command line argument_ to load a
module and then start the interpreter with the module `timeit` pre-loaded.
That way you don't have to type `import <modulename>` after starting the
interpreter. It is also using the `-s` command line argument to specify that
the user-site-packages directory should not be added to `sys.path`.

For more information on command line arguments for the python interpreter,
check out the [official
documentation.](http://docs.python.org/2/using/cmdline.html)

