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"""Spawn a command with pipes to its stdin, stdout, and optionally stderr.
The normal os.popen(cmd, mode) call spawns a shell command and provides a
file interface to just the input or output of the process depending on
whether mode is 'r' or 'w'. This module provides the functions popen2(cmd)
and popen3(cmd) which return two or three pipes to the spawned command.
"""
import os
import sys
__all__ = ["popen2", "popen3", "popen4"]
try:
MAXFD = os.sysconf('SC_OPEN_MAX')
except (AttributeError, ValueError):
MAXFD = 256
_active = []
def _cleanup():
for inst in _active[:]:
if inst.poll(_deadstate=sys.maxint) >= 0:
try:
_active.remove(inst)
except ValueError:
# This can happen if two threads create a new Popen instance.
# It's harmless that it was already removed, so ignore.
pass
class Popen3:
"""Class representing a child process. Normally instances are created
by the factory functions popen2() and popen3()."""
sts = -1 # Child not completed yet
def __init__(self, cmd, capturestderr=False, bufsize=-1):
"""The parameter 'cmd' is the shell command to execute in a
sub-process. On UNIX, 'cmd' may be a sequence, in which case arguments
will be passed directly to the program without shell intervention (as
with os.spawnv()). If 'cmd' is a string it will be passed to the shell
(as with os.system()). The 'capturestderr' flag, if true, specifies
that the object should capture standard error output of the child
process. The default is false. If the 'bufsize' parameter is
specified, it specifies the size of the I/O buffers to/from the child
process."""
_cleanup()
self.cmd = cmd
p2cread, p2cwrite = os.pipe()
c2pread, c2pwrite = os.pipe()
if capturestderr:
errout, errin = os.pipe()
self.pid = os.fork()
if self.pid == 0:
# Child
os.dup2(p2cread, 0)
os.dup2(c2pwrite, 1)
if capturestderr:
os.dup2(errin, 2)
self._run_child(cmd)
os.close(p2cread)
self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
os.close(c2pwrite)
self.fromchild = os.fdopen(c2pread, 'r', bufsize)
if capturestderr:
os.close(errin)
self.childerr = os.fdopen(errout, 'r', bufsize)
else:
self.childerr = None
def __del__(self):
# In case the child hasn't been waited on, check if it's done.
self.poll(_deadstate=sys.maxint)
if self.sts < 0:
if _active is not None:
# Child is still running, keep us alive until we can wait on it.
_active.append(self)
def _run_child(self, cmd):
if isinstance(cmd, basestring):
cmd = ['/bin/sh', '-c', cmd]
for i in range(3, MAXFD):
try:
os.close(i)
except OSError:
pass
try:
os.execvp(cmd[0], cmd)
finally:
os._exit(1)
def poll(self, _deadstate=None):
"""Return the exit status of the child process if it has finished,
or -1 if it hasn't finished yet."""
if self.sts < 0:
try:
pid, sts = os.waitpid(self.pid, os.WNOHANG)
# pid will be 0 if self.pid hasn't terminated
if pid == self.pid:
self.sts = sts
except os.error:
if _deadstate is not None:
self.sts = _deadstate
return self.sts
def wait(self):
"""Wait for and return the exit status of the child process."""
if self.sts < 0:
pid, sts = os.waitpid(self.pid, 0)
# This used to be a test, but it is believed to be
# always true, so I changed it to an assertion - mvl
assert pid == self.pid
self.sts = sts
return self.sts
class Popen4(Popen3):
childerr = None
def __init__(self, cmd, bufsize=-1):
_cleanup()
self.cmd = cmd
p2cread, p2cwrite = os.pipe()
c2pread, c2pwrite = os.pipe()
self.pid = os.fork()
if self.pid == 0:
# Child
os.dup2(p2cread, 0)
os.dup2(c2pwrite, 1)
os.dup2(c2pwrite, 2)
self._run_child(cmd)
os.close(p2cread)
self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
os.close(c2pwrite)
self.fromchild = os.fdopen(c2pread, 'r', bufsize)
if sys.platform[:3] == "win" or sys.platform == "os2emx":
# Some things don't make sense on non-Unix platforms.
del Popen3, Popen4
def popen2(cmd, bufsize=-1, mode='t'):
"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
be a sequence, in which case arguments will be passed directly to the
program without shell intervention (as with os.spawnv()). If 'cmd' is a
string it will be passed to the shell (as with os.system()). If
'bufsize' is specified, it sets the buffer size for the I/O pipes. The
file objects (child_stdout, child_stdin) are returned."""
w, r = os.popen2(cmd, mode, bufsize)
return r, w
def popen3(cmd, bufsize=-1, mode='t'):
"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
be a sequence, in which case arguments will be passed directly to the
program without shell intervention (as with os.spawnv()). If 'cmd' is a
string it will be passed to the shell (as with os.system()). If
'bufsize' is specified, it sets the buffer size for the I/O pipes. The
file objects (child_stdout, child_stdin, child_stderr) are returned."""
w, r, e = os.popen3(cmd, mode, bufsize)
return r, w, e
def popen4(cmd, bufsize=-1, mode='t'):
"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
be a sequence, in which case arguments will be passed directly to the
program without shell intervention (as with os.spawnv()). If 'cmd' is a
string it will be passed to the shell (as with os.system()). If
'bufsize' is specified, it sets the buffer size for the I/O pipes. The
file objects (child_stdout_stderr, child_stdin) are returned."""
w, r = os.popen4(cmd, mode, bufsize)
return r, w
else:
def popen2(cmd, bufsize=-1, mode='t'):
"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
be a sequence, in which case arguments will be passed directly to the
program without shell intervention (as with os.spawnv()). If 'cmd' is a
string it will be passed to the shell (as with os.system()). If
'bufsize' is specified, it sets the buffer size for the I/O pipes. The
file objects (child_stdout, child_stdin) are returned."""
inst = Popen3(cmd, False, bufsize)
return inst.fromchild, inst.tochild
def popen3(cmd, bufsize=-1, mode='t'):
"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
be a sequence, in which case arguments will be passed directly to the
program without shell intervention (as with os.spawnv()). If 'cmd' is a
string it will be passed to the shell (as with os.system()). If
'bufsize' is specified, it sets the buffer size for the I/O pipes. The
file objects (child_stdout, child_stdin, child_stderr) are returned."""
inst = Popen3(cmd, True, bufsize)
return inst.fromchild, inst.tochild, inst.childerr
def popen4(cmd, bufsize=-1, mode='t'):
"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
be a sequence, in which case arguments will be passed directly to the
program without shell intervention (as with os.spawnv()). If 'cmd' is a
string it will be passed to the shell (as with os.system()). If
'bufsize' is specified, it sets the buffer size for the I/O pipes. The
file objects (child_stdout_stderr, child_stdin) are returned."""
inst = Popen4(cmd, bufsize)
return inst.fromchild, inst.tochild
__all__.extend(["Popen3", "Popen4"])
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