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I'm trying to pipe data that starts life in an array('B') object
through several processes. The code below is a simplified example. The
data makes it through, but the wait() always hangs. Is there a better
way to indicate src.stdin has reach EOF?

from subprocess import Popen, PIPE
from array import array

arr = array('B')
arr.fromstring("hello\n")

src = Popen( ["cat"], stdin=PIPE, stdout=PIPE)
dst = Popen( ["cat"], stdin=src.stdout)
arr.tofile(src.stdin)
src.stdin.close()
dst.wait()