Chosing between sys.argv and sys.stdin

[Steve Holden]

"Syn.Terra" wrote:
> 
> I've got a Python script that I want to be used either with commandline
> arguments or using stdin (most likely by piping). My question is, what's
> the simplest way to code that sort of conditional? My current script
> fragment looks like this:
> 
> import sys
> try:
>         text = sys.argv[1]
> except IndexError:
>         print "usage: ..."
>         sys.exit()
> 
Obviously, you will get the IndexError if len(sys.argv) < 2
so this is the key condition to code around.

> How would I add something that says "use sys.stdin if they don't include
> commandline arguments, but if neither is present, print the error
> message"? Right now, if it calls sys.stdin.read() and it wasn't piped
> into (like calling "spam.py" rather than "cat file | spam.py") it just
> sits there until I hit ctrl-d.
> 
Probably what you need is something like the following, which
will work for a single file name.  You can easily extend it to
multiple filenames (left as an exercise to the reader...)

if len(sys.argv) < 1:
	myfile = sys.stdin
else:
	try:
		myfile = open(sys.argv[1], 'r')
	except:
		print "Could not open file", sys.argv[1]
		sys.exit(-1)

> Note: I don't frequent the newsgroup, so if you could send replies to
> dream at aevum.net, I'd be greatly appreciative.
> 
> ----
> Syn.Terra
> Aevum Industries
> http://www.aevum.net

Posted and mailed.

regards
 Steve
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