[Tutor] Sys.stdin Question

[Damon Timm]

On Tue, Jan 13, 2009 at 8:28 PM, Alan Gauld <alan.gauld at btinternet.com> wrote:
> The way other Unix style programs deal with this is to write the code
> to read from a general file and if you want to use stdin provide an
> argument of '-':

That's a good idea, actually -- I hadn't thought of that.  Although I
use that "-" a lot in command line programs ...  It would force
someone to be specific about what it was they wanted the script to do
... then, I guess, I can just have it do an if statement that asks: if
args[0] == "-" then ... blah.  I may do that ... the script, itself,
actually handles attachments, too ... so I could use that flag, also,
to say: attach the standard out to an email.

On Tue, Jan 13, 2009 at 8:45 PM, John Fouhy <john at fouhy.net> wrote:
> This might work:
>
> import select, sys
> def isData():
>            return select.select([sys.stdin], [], [], 0) ==
> ([sys.stdin], [], [])
>
> if isData():
>  print 'You typed:', sys.stdin.read()
> else:
>  print 'Nothing to see here.'

Oh ho ho!  Very neat!  I will have to head over to the python docs to
see what that is but it seems to work!

> I say "might" because it is OS-dependent, but I guess you are using unix/linux.

Yea - you guessed right.

> Source: http://www.darkcoding.net/software/non-blocking-console-io-is-not-possible/
>
> I found that by searching for "python stdin non-blocking".  This is
> because "blocking" is jargon for "waiting until something happens".
> In this case, stdin.read() is blocking until it sees some data with an
> EOF.

Thanks for that tip -- as you probably guessed, google wasn't turning
up too many results for me.  But this is working now.  However ...
reading the next comment has me thinking again:

On Tue, Jan 13, 2009 at 8:55 PM, Steve Willoughby <steve at alchemy.com> wrote:
> This is playing a dangerous game, though, of introducing a race condition.
>  Is there nothing on the standard input RIGHT NOW because the source on
> the other end of the pipe hasn't managed to generate anything yet, or
> because there's nothing piped?
>
> A better approach is either to explicitly specify whether to read from
> stdin or a file, as Alan demonstrated (and the fileinput module implements
> this for you, by the way), or to see if stdin is connected to a terminal
> or not.  So instead of seeing if anything's showing up (and introducing
> timing dependencies and uncertainty), see if it's attached to a real
> terminal at all.  On Unix, os.isatty(sys.stdin) will tell you this.

Does this concern still apply with John's suggestion?  I just tested
it in my little application and didn't have an issue ... of course, I
only ran a couple different command line items before throwing up my
hands in celebration.

I can go to using the "-" option ... although, to be honest, I like
the idea of the script thinking for itself ... that is: if there is
stdin, use it -- if not, not ... and, I was thinking of attaching the
stdin as a text file, if present.  And not attaching anything, if not.


Thanks everyone!