On the other hand, we will silently break all those applications which
are out there relying on the fact that a pipe is an unbuffered device.
You might consider it for Python 3.0, but I don't know if it is a good
idea for Python 2.x. The documentation of subprocess.Popen clear states
that the default is unbuffered, bufsize=0. I quote from
http://docs.python.org/library/subprocess.html:

bufsize, if given, has the same meaning as the corresponding argument to
the built-in open() function: 0 means unbuffered, 1 means line buffered,
any other positive value means use a buffer of (approximately) that
size. A negative bufsize means to use the system default, which usually
means fully buffered. The default value for bufsize is 0 (unbuffered).