[Tutor] opening a file directly from memory
alan.gauld at btinternet.com
Tue Nov 17 22:33:46 CET 2009
<mjekl at iol.pt> wrote
>>> If you do you can call it explicitly, but if you do not then you
>>> need to find a way of getting the OS to tell you, or to leave it to
>>> the OS.
> I'm interested in nthis for the sake of generalizing (which is
> better). How can I get the OS to tell me which program to use.
> alternatively, how to tell the OS to open it - assuming that since the
> os knows which program to use it will just use it
This is where it gets messy.
The solution depends on the OS. If its Windows you can use Startfile.
If its MacOS you can interrogate the package manifest.
If its another Unix you can use any of several options depending on the
flavour. The simplest is, I think, the file command, then if its a
text file you can check the shebang line at the top of the file. But
modern Unices, like Linux have file association tables - but these
are often associated with the desktop environment - KDE, Gnome etc.
Finally for text files you should check the EDITOR and VISUAL
environment variables - although these are increasingly not
used or respected nowadays.
So you could write a program that checked the OS and then tried
all of these options to identify the host application. But even then
you are not guaranteed to succeed!
Finally you can try just running the file via os.system or the
subprocess module and see what happens!
But there is no foolproof way of doing it on all OS. That's why
its easier if you either know what app to use or create a
config file such that the user can specify the app at install time.
On unix that would traditionally be called .myapprc aand be
stored in each users home directory.
On Windows it would either be a registry entry or a myapp.ini file,
usually stored in the Windows directory or (better IMHO but against
MS guidelines) in the app directory.
Author of the Learn to Program web site
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