dmoore <[EMAIL PROTECTED]> wrote: > I've seen the following issue come up in multiple posts to this > mailing list: > > I have a python program that spawns a child process with popen or > popen2 or popen3 or popen2.popen2 etc. > the child process is interactive: it asks for input then spits out > some output, asks for more input then spits out some output. for > example, consider the trivial child program: > > print "welcome" > print ">", > s=raw_input() > while s!='exit': > print "you entered:",s > print ">", > s=raw_input() > > Now I may be completely wrong about this (I did play with popen for a > very long time before writing this message), but it appears that none > of the popen variants allow for a sequence of reads and writes to/from > this child. that is, if I read from the open pipe's output I will > never be able to write the input for the child because the parent > program will block on read until eof (I will have similar blocking > problems if I start with write - using readline does not seem to > help).
You are correct. > the standard proposed remedy I have seen on this list is to use Unix- > only select/fctl, or otherwise dig into the bowls of the win32 api, or > download some half-complete sourceforge process control project. If you are referring to pexpect I've found it works well - unix only though. I've not noticed it being half complete. There is also a recipe for a non-blocking subprocess - see http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/440554 > All well and good, but unsatisfying for writing platform independent code. > > it turns out that there is at least one open source multi-platform > (read: win32/linux) api that does handle synchronous I/O with the > child: wxWidgets and wxPython using the class wxProcess. Now the > wxWidgets implementation is far from perfect, but it at least allows a > program to test for new input on the child's stdout and read stdout/ > write stdout in a non-blocking way. Interesting I didn't know about that - I shall try it! > However, I find it frustrating > that I have to import wx just to have useable interactive pipes in my > python scripts when I would expect this to be part of the native > python implementation. > > Anybody have any thoughts on this? Do I have my story straight? (the > popen variants can't handle this case and there are no other > alternatives in the standard python distro) Is there some place I can > submit this as a feature request? (Python dev?) The non-blocking subprocess would make a good start for a stdlib submission. It should really optionally use ptys under unix too otherwise you'll never be able to script passwd etc. An interface a bit like pexpect wpuld be useful too (ie scan for these regexps or timeout and return a match object). -- Nick Craig-Wood <[EMAIL PROTECTED]> -- http://www.craig-wood.com/nick -- http://mail.python.org/mailman/listinfo/python-list
