cpython/Lib/popen2.py
Guido van Rossum 54f22ed30b More trivial comment -> docstring transformations by Ka-Ping Yee,
who writes:

Here is batch 2, as a big collection of CVS context diffs.
Along with moving comments into docstrings, i've added a
couple of missing docstrings and attempted to make sure more
module docstrings begin with a one-line summary.

I did not add docstrings to the methods in profile.py for
fear of upsetting any careful optimizations there, though
i did move class documentation into class docstrings.

The convention i'm using is to leave credits/version/copyright
type of stuff in # comments, and move the rest of the descriptive
stuff about module usage into module docstrings.  Hope this is
okay.
2000-02-04 15:10:34 +00:00

128 lines
4.1 KiB
Python

"""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
import string
MAXFD = 256 # Max number of file descriptors (os.getdtablesize()???)
_active = []
def _cleanup():
for inst in _active[:]:
inst.poll()
class Popen3:
"""Class representing a child process. Normally instances are created
by the factory functions popen2() and popen3()."""
def __init__(self, cmd, capturestderr=0, bufsize=-1):
"""The parameter 'cmd' is the shell command to execute in a
sub-process. 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."""
if type(cmd) == type(''):
cmd = ['/bin/sh', '-c', 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.close(0)
os.close(1)
if os.dup(p2cread) <> 0:
sys.stderr.write('popen2: bad read dup\n')
if os.dup(c2pwrite) <> 1:
sys.stderr.write('popen2: bad write dup\n')
if capturestderr:
os.close(2)
if os.dup(errin) <> 2: pass
for i in range(3, MAXFD):
try:
os.close(i)
except: pass
try:
os.execvp(cmd[0], cmd)
finally:
os._exit(1)
# Shouldn't come here, I guess
os._exit(1)
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
self.sts = -1 # Child not completed yet
_active.append(self)
def poll(self):
"""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)
if pid == self.pid:
self.sts = sts
_active.remove(self)
except os.error:
pass
return self.sts
def wait(self):
"""Wait for and return the exit status of the child process."""
pid, sts = os.waitpid(self.pid, 0)
if pid == self.pid:
self.sts = sts
_active.remove(self)
return self.sts
def popen2(cmd, bufsize=-1):
"""Execute the shell command 'cmd' in a sub-process. If 'bufsize' is
specified, it sets the buffer size for the I/O pipes. The file objects
(child_stdout, child_stdin) are returned."""
_cleanup()
inst = Popen3(cmd, 0, bufsize)
return inst.fromchild, inst.tochild
def popen3(cmd, bufsize=-1):
"""Execute the shell command 'cmd' in a sub-process. 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."""
_cleanup()
inst = Popen3(cmd, 1, bufsize)
return inst.fromchild, inst.tochild, inst.childerr
def _test():
teststr = "abc\n"
print "testing popen2..."
r, w = popen2('cat')
w.write(teststr)
w.close()
assert r.read() == teststr
print "testing popen3..."
r, w, e = popen3(['cat'])
w.write(teststr)
w.close()
assert r.read() == teststr
assert e.read() == ""
for inst in _active[:]:
inst.wait()
assert not _active
print "All OK"
if __name__ == '__main__':
_test()