redirecting stdin with Python scripts under win2k (solution)

[Bengt Richter]

On Thu, 14 Mar 2002 11:38:52 +0000, Dale Strickland-Clark <dale at riverhall.NOTHANKS.co.uk> wrote:

>I'm sure you're very pleased with that but I don't see the point.
>
>If I want to run a Python program, I just type the name of it at a
>command prompt.
>
Yes, but that is not the key point of Syver's contribution.

>A few prerequisites need to be in place but some of these happen
>during install:
>
>1. The directory containing the script needs to be in your PATH
>environment var or be the current directory.
>2. PATHEXT environment var needs to contain ".PY;.PYC;.PYW"
>3. The Python exes need to be associated with the Python file types.
>
>Once you get all the above right, you just type:
>
>C:\> wibble args
>
>and it runs:
>
>"C:\Python21\python.exe" "wibble.py" args
>
You are missing the key point, which is about redirection of i/o.
If you tried to use your wibble thus:

    wibble args > outputfile

You would get a zero length output file on NT4.
Syver solved _that_ problem without using a separate wrapper.

I would have been pleased to have thought of it, especially since
I recently posted separate wrapping solutions. Plus, not long ago I
saw a post using a similar technique with a linux shell in a cgi
context, and I didn't make the connection. Syver either re-invented
that (for windows) or made the connection and reformulated it. Either
way, I think he deserves credit, not a comment like "I'm sure you're
very pleased with that ..."

>This only works with Win NT/2K/XP. As for 95/98/ME, well it's easier
>not to bother, really.
>
>Disguising your Python programs as batch files is going to knacker any
>attempt your editor may make to help with syntax highlighting and
>suchlike.
That may be a downside for editors that decide on the basis of file extension,
but you are not obligated to do all your scripts this way ;-)

Being able to invoke a script concisely and have its output
redirectable is something you want for full flexibility e.g. in putting
customized scripted build steps in the VC++ IDE for e.g., customizing
building Python from source on windows.

Being able to wrap without a separate file is a good thing IMO, although
for scripts that are supposed to be verbatim (e.g. signed etc) portable to
*nix, you'd want to continue using separate wrappers in windows.

<interesting side note>
If you use a hash, e.g. MD5, or PGP to sign/validate a script, should it
be based on canonicalizing to unix format (i.e., \n vs \r\n or \r)?
I imagine the XML folks must have decided something. ...but I don't have
time to google every stray question that pops to mind ;-)
</interesting side note>

>
>Also, FYI, I think all the command extensions you mention were
>introduced with NT 4.
Yes, the technique works on NT4, which pleases me ;-)
The cmd.exe batch command line syntax is really horrid, weak, and badly
documented though, so it's nice to be able to transition to Python in one line!

Regards,
Bengt Richter