[issue4194] Miserable subprocess.Popen performance

[Skip Montanaro]

Skip Montanaro <skip at pobox.com> added the comment:

>> Using a nonzero bufsize parameter makes all the difference in the
    >> world:
    ...

In fact, looking at posix_popen in posixmodule.c it appears the default
value for bufsize there is -1, implying that I/O is fully buffered.

Even if the default bufsize value for subprocess.Popen is not changed its
documentation should be corrected to reflect the different default values
for bufsize between os.popen and subprocess.Popen:

    Replacing os.popen*
    -------------------
    pipe = os.popen(cmd, mode='r', [bufsize])
    ==>
    pipe = Popen(cmd, shell=True, bufsize=bufsize, stdout=PIPE).stdout

    If you use the default bufsize with os.popen you must set bufsize to -1
    when creating a Popen object.  Otherwise your I/O will be unbuffered and
    you will be disappointed at the I/O performance.

----------
assignee:  -> georg.brandl
components: +Documentation, Library (Lib)
nosy: +georg.brandl
versions: +Python 2.7, Python 3.0

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<http://bugs.python.org/issue4194>
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