A tale of two execs

[aha]

Hello All,
  So below is my naive attempt at the wrapper, it is only half baked
since I am no master at Interprocess communication... I know that it
is lacking a lot of things comment greatly appreciated:

#!/usr/bin/env python

import os, sys, re, exceptions
try:
    import subprocess
except ImportError:
    import popen2
    subprocess = None

PIPE = 10
SOUT = 11

class Runner:
    def __init__(self):
        self.stdout = None
        self.stdin = None
        self.stderr = None
        self.pid = None
        self.process = None

    def runCmdLine(self, args, executable=None, stdin=None,
stdout=None, stderr=None, preexec_fn=None,
                   close_fds=False, shell=False,cwd=None, env=None):
        """
        args -- a string, or a sequence of program arguments. The
argument to execute is
        normally the first item in the args sequence or the string if
a string is given,
        but can be explicitly set by using the executable argument.

        executable -- string to be executed

        stdin, stdout, stderr -- value of standard input, standard
output, and standard
        error file handles.  None implies no redirection. Valid values
are PIPE, an existing
        file descriptor (a positive integer), an existing file object,
and None.

        shell -- specifies whether command should be executed through
shell

        cwd -- specifies whether, childs current directory will be
changed to cwd

        env -- A map that specifies the environment variables in child
process
        that will be overwritten

        NOTE: Depending on the modules available, some arguments may
not be used.
        """
        if subprocess:
            # Use subprocess to exec functions
            if stdin == PIPE:
                sin = subprocess.PIPE
            else:
                # NOTE: User may input invalid values that will cause
exceptions
                sin = stdin
            if stdout == PIPE:
                sout = subprocess.PIPE
            else:
                sout = stdout
            if stderr == SOUT:
                serr = subprocess.STDOUT
            else:
                serr = stderr

            self.process = subprocess.Popen(args, stdin=sin,
stdout=sout, stderr=serr,
 
preexec_fn=preexec_fn,close_fds=close_fds, shell=shell,
                                            env=env, cwd=cwd)
            self.pid = self.process.pid
           # Add attributes stdin, stdout, and stderr
            self.stdin = self.process.stdin
            self.stdout = self.process.stdout
            self.stderr = self.process.stderr
        else:
            # Use popen2 to exec functions
            # Determine which form of popen2 to use
            if stderr == SOUT or stderr == None:
                self.process =  popen2.Popen4(args)
                self.stdin = self.process.tochild
                self.stdout = self.process.fromchild
                self.stderr = None
            else:
                self.process =  popen2.Popen3(args)
                self.stdin = self.process.tochild
                self.stdout = self.process.fromchild
                self.stderr = self.process.childerr

            self.pid = self.process.pid

    def wait(self,):
        """
        Waits for and returns the status code of the child process.
        """
        return self.process.wait()

    def poll(self,):
        """
        Returns -1 if the child process hasn't completed yet, or it's
return code
        otherwise
        """
        return self.process.poll()

Aquil

On Feb 23, 2:10 pm, Christian Heimes <li... at cheimes.de> wrote:
> aha wrote
>
> > def runner(cmd, stdin, stdout, ...):
> >   try:
> >     import subprocess
> >     sbm = 1
> >   except:
> >     sbm = 0
>
> >   # Now do something
> >   if sbm:
> >     process = subporcess(...)
> >   else:
> >     import popen2
> >     process = popen2.Popen4(...)
>
> > Has anyone else run into a situation similar to this one?
>
> The canonical way for your try/except clause is:
>
> try:
>     import subprocess
> except ImportError:
>     subprocess = None
>
> ...
>
> if subprocess is not None:
>     ...
> else:
>     ...
>
> Christian