[Tutor] Command line scripts

[ALAN GAULD]

> The following line is what I mean by calling a  command line from within the 
>app
> using subprocess.
> 
> self.espeak =  subprocess.Popen(['espeak', word],stdout  =
> subprocess.PIPE).communicate()[0]

OK, Now I understand. 
You want to call an external application from within your code 
via subprocess. And you want to know if that will work ok in a 
wxPython application?

> >> In other words,  is a command line app different from
> >> bindings in a compiled  app?

When you call an app using subprocess it spawns an entirely 
separate process in the OS. There is no linkage to your process 
apart from the redirection of stdin/stdout/stderr back to your 
app instead of to a console.

> > So-called exe generators simply bundle the interpreter  witrh
> > the code and auto run it.
> 
> So it's basically just installing  a sandbox version of python?

Sort of, its a minimalist version of python with only the modules 
needed to run the app. And you can't run the interpreter on its 
own you can only run the packaged app.

> Which ultimately is, if I have a standalone  application, that doesn't
> come from a command line terminal launching(which I  haven't gotten to
> yet), is using the command line calls going through  subprocess going
> to be called without the terminal, or will it open a  terminal
> automatically to make those calls?

The app (eSpeak in your example) will see your app as its "console". 
That is, it will send all output to your app and read all input from your 
app (so you need to make sure it gets any input it is expecting!)
The other thing to watch in a wxPython (or any other GUI framework) 
is that if the app runs for a long time your app may "freeze" from 
the user's perspective, so you may want to run it in the background 
or as a separate thread in your app.

> Or will all of my python  apps need to have a command line terminal
> open to launch them. 

No, your app takes over the job of the terminal. When you launch 
a program from the terninal the terminal app(for it is just an app like 
any other) is doing the same as you, it is spawning a subprocess 
that sends its output back to the teminal for it to display.

In fact you might find it a useful exercise to build a very basic terminal 
app in wxPython first. Read commands from a command input field 
and display the output in a text widget... Execute the commands 
via subprocess. Its a good way to get used to using subprocess 
and experimenting with its various options. If you are very keen 
you can start adding command history and search etc to it too...

HTH,

Alan G.