subprocess keeps other side of child pipe open, making
use of SIGPIPE to terminate writers in a pipeline
not possible.

This is probably a matter of documentation or
providing a method to link up processes, as 
the parent end of the pipe must remain open
until it is connected to the next process in
the pipeline.

An option to enable sigpipe in child would be
nice.

Simple example attached.

One easy solution is to simply close the pipe in the parent after starting both processes, before calling p1.wait():

p1.stdout.close()

It's not "perfect", though, p1 will execute a while before recieving SIGPIPE. For a perfect solution, it would be necessary to close the pipe end in the parent after the fork but before the exec in the child. This would require some kind of synchronization. 

Moving to feature request. 

Confirmed on trunk and py3k.

The need to call p1.stdout.close() has now been documented as part of issue7678.  Python 3.2's subprocess also has restore_signals=True as its default behavior so SIGPIPE is restored by default.

I do not think it is appropriate to to add the synchronization Peter suggested to the subprocess module to optimize that close call.  The potential delay due to python having to call p1.stdout.close() is non-fatal and should be assumed to exist anyways as you can't guarantee when an async event like a signal (in this case SIGPIPE) will actually reach the other process.