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Issue #5870: Add subprocess.DEVNULL constant.

This commit is contained in:
Ross Lagerwall 2011-03-16 18:40:25 +02:00
parent 09bb8f46aa
commit ba102ec10d
4 changed files with 66 additions and 7 deletions
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23
Doc/library/subprocess.rst
View File

@ -125,12 +125,14 @@ This module defines one class called :class:`Popen`:
*stdin*, *stdout* and *stderr* specify the executed programs' standard input,
standard output and standard error file handles, respectively. Valid values
are :data:`PIPE`, an existing file descriptor (a positive integer), an
existing :term:`file object`, and ``None``. :data:`PIPE` indicates that a
new pipe to the child should be created. With ``None``, no redirection will
occur; the child's file handles will be inherited from the parent. Additionally,
*stderr* can be :data:`STDOUT`, which indicates that the stderr data from the
applications should be captured into the same file handle as for stdout.
are :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a positive
integer), an existing :term:`file object`, and ``None``. :data:`PIPE`
indicates that a new pipe to the child should be created. :data:`DEVNULL`
indicates that the special file :data:`os.devnull` will be used. With ``None``,
no redirection will occur; the child's file handles will be inherited from
the parent. Additionally, *stderr* can be :data:`STDOUT`, which indicates
that the stderr data from the applications should be captured into the same
file handle as for stdout.
If *preexec_fn* is set to a callable object, this object will be called in the
child process just before the child is executed.
@ -229,6 +231,15 @@ This module defines one class called :class:`Popen`:
Added context manager support.
.. data:: DEVNULL
Special value that can be used as the *stdin*, *stdout* or *stderr* argument
to :class:`Popen` and indicates that the special file :data:`os.devnull`
will be used.
.. versionadded:: 3.3
.. data:: PIPE
Special value that can be used as the *stdin*, *stdout* or *stderr* argument

23
Lib/subprocess.py
View File

@ -431,7 +431,7 @@ else:
return fds
__all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
"getoutput", "check_output", "CalledProcessError"]
"getoutput", "check_output", "CalledProcessError", "DEVNULL"]
if mswindows:
from _subprocess import CREATE_NEW_CONSOLE, CREATE_NEW_PROCESS_GROUP
@ -456,6 +456,7 @@ def _cleanup():
PIPE = -1
STDOUT = -2
DEVNULL = -3
def _eintr_retry_call(func, *args):
@ -800,6 +801,10 @@ class Popen(object):
# Child is still running, keep us alive until we can wait on it.
_active.append(self)
def _get_devnull(self):
if not hasattr(self, '_devnull'):
self._devnull = os.open(os.devnull, os.O_RDWR)
return self._devnull
def communicate(self, input=None, timeout=None):
"""Interact with process: Send data to stdin. Read data from
@ -889,6 +894,8 @@ class Popen(object):
p2cread, _ = _subprocess.CreatePipe(None, 0)
elif stdin == PIPE:
p2cread, p2cwrite = _subprocess.CreatePipe(None, 0)
elif stdin == DEVNULL:
p2cread = msvcrt.get_osfhandle(self._get_devnull())
elif isinstance(stdin, int):
p2cread = msvcrt.get_osfhandle(stdin)
else:
@ -902,6 +909,8 @@ class Popen(object):
_, c2pwrite = _subprocess.CreatePipe(None, 0)
elif stdout == PIPE:
c2pread, c2pwrite = _subprocess.CreatePipe(None, 0)
elif stdout == DEVNULL:
c2pwrite = msvcrt.get_osfhandle(self._get_devnull())
elif isinstance(stdout, int):
c2pwrite = msvcrt.get_osfhandle(stdout)
else:
@ -917,6 +926,8 @@ class Popen(object):
errread, errwrite = _subprocess.CreatePipe(None, 0)
elif stderr == STDOUT:
errwrite = c2pwrite
elif stderr == DEVNULL:
errwrite = msvcrt.get_osfhandle(self._get_devnull())
elif isinstance(stderr, int):
errwrite = msvcrt.get_osfhandle(stderr)
else:
@ -1026,6 +1037,8 @@ class Popen(object):
c2pwrite.Close()
if errwrite != -1:
errwrite.Close()
if hasattr(self, '_devnull'):
os.close(self._devnull)
# Retain the process handle, but close the thread handle
self._child_created = True
@ -1159,6 +1172,8 @@ class Popen(object):
pass
elif stdin == PIPE:
p2cread, p2cwrite = _create_pipe()
elif stdin == DEVNULL:
p2cread = self._get_devnull()
elif isinstance(stdin, int):
p2cread = stdin
else:
@ -1169,6 +1184,8 @@ class Popen(object):
pass
elif stdout == PIPE:
c2pread, c2pwrite = _create_pipe()
elif stdout == DEVNULL:
c2pwrite = self._get_devnull()
elif isinstance(stdout, int):
c2pwrite = stdout
else:
@ -1181,6 +1198,8 @@ class Popen(object):
errread, errwrite = _create_pipe()
elif stderr == STDOUT:
errwrite = c2pwrite
elif stderr == DEVNULL:
errwrite = self._get_devnull()
elif isinstance(stderr, int):
errwrite = stderr
else:
@ -1374,6 +1393,8 @@ class Popen(object):
os.close(c2pwrite)
if errwrite != -1 and errread != -1:
os.close(errwrite)
if hasattr(self, '_devnull'):
os.close(self._devnull)
# Wait for exec to fail or succeed; possibly raising an
# exception (limited in size)

25
Lib/test/test_subprocess.py
View File

@ -323,6 +323,31 @@ class ProcessTestCase(BaseTestCase):
rc = subprocess.call([sys.executable, "-c", cmd], stdout=1)
self.assertEqual(rc, 2)
def test_stdout_devnull(self):
p = subprocess.Popen([sys.executable, "-c",
'for i in range(10240):'
'print("x" * 1024)'],
stdout=subprocess.DEVNULL)
p.wait()
self.assertEqual(p.stdout, None)
def test_stderr_devnull(self):
p = subprocess.Popen([sys.executable, "-c",
'import sys\n'
'for i in range(10240):'
'sys.stderr.write("x" * 1024)'],
stderr=subprocess.DEVNULL)
p.wait()
self.assertEqual(p.stderr, None)
def test_stdin_devnull(self):
p = subprocess.Popen([sys.executable, "-c",
'import sys;'
'sys.stdin.read(1)'],
stdin=subprocess.DEVNULL)
p.wait()
self.assertEqual(p.stdin, None)
def test_cwd(self):
tmpdir = tempfile.gettempdir()
# We cannot use os.path.realpath to canonicalize the path,

2
Misc/NEWS
View File

@ -72,6 +72,8 @@ Core and Builtins
Library
-------
- Issue #5870: Add `subprocess.DEVNULL` constant.
- Issue #11133: fix two cases where inspect.getattr_static can trigger code
execution. Patch by Andreas Stührk.