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Fixes issue #17488: Change the subprocess.Popen bufsize parameter default value

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from unbuffered (0) to buffering (-1) to match the behavior existing code
expects and match the behavior of the subprocess module in Python 2 to avoid
introducing hard to track down bugs.
This commit is contained in:
Gregory P. Smith 2013-03-23 12:00:00 -07:00
commit 4a8ea9e2a6
4 changed files with 55 additions and 19 deletions
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23
Doc/library/subprocess.rst
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@ -356,7 +356,7 @@ are able to handle the less common cases not covered by the convenience
functions.
.. class:: Popen(args, bufsize=0, executable=None, stdin=None, stdout=None, \
.. class:: Popen(args, bufsize=-1, executable=None, stdin=None, stdout=None, \
stderr=None, preexec_fn=None, close_fds=True, shell=False, \
cwd=None, env=None, universal_newlines=False, \
startupinfo=None, creationflags=0, restore_signals=True, \
@ -428,17 +428,20 @@ functions.
untrusted input. See the warning under :ref:`frequently-used-arguments`
for details.
*bufsize*, if given, has the same meaning as the corresponding argument to the
built-in open() function: :const:`0` means unbuffered, :const:`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 :const:`0` (unbuffered).
*bufsize* will be supplied as the corresponding argument to the :meth:`io.open`
function when creating the stdin/stdout/stderr pipe file objects:
:const:`0` means unbuffered (read and write are one system call and can return short),
:const:`1` means line buffered, any other positive value means use a buffer of
approximately that size. A negative bufsize (the default) means
the system default of io.DEFAULT_BUFFER_SIZE will be used.
.. note::
.. versionchanged:: 3.2.4, 3.3.1
If you experience performance issues, it is recommended that you try to
enable buffering by setting *bufsize* to either -1 or a large enough
positive value (such as 4096).
*bufsize* now defaults to -1 to enable buffering by default to match the
behavior that most code expects. In 3.2.0 through 3.2.3 and 3.3.0 it
incorrectly defaulted to :const:`0` which was unbuffered and allowed
short reads. This was unintentional and did not match the behavior of
Python 2 as most code expected.
The *executable* argument specifies a replacement program to execute. It
is very seldom needed. When ``shell=False``, *executable* replaces the