[Tutor] Popen was deprecated since Python 2.6, now what?

[Ken G.]

On 02/16/2015 06:26 PM, Alan Gauld wrote:
> On 16/02/15 21:26, Ken G. wrote:
>> I have not been able to figure out on how to use a
>> subprocess in place of my former popen. I have been
>> reading the new materials on the subprocess  all day
>> and it is still not quite understandable.
>
>
> Here is what the docs say:
>
> ###########################################################
> 17.5.5.5. Replacing os.popen(), os.popen2(), os.popen3()
>
> (child_stdin, child_stdout) = os.popen2(cmd, mode, bufsize)
> ==>
> p = Popen(cmd, shell=True, bufsize=bufsize,
>           stdin=PIPE, stdout=PIPE, close_fds=True)
> (child_stdin, child_stdout) = (p.stdin, p.stdout)
>
>
>
>
> (child_stdin,
>  child_stdout,
>  child_stderr) = os.popen3(cmd, mode, bufsize)
> ==>
> p = Popen(cmd, shell=True, bufsize=bufsize,
>           stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True)
> (child_stdin,
>  child_stdout,
>  child_stderr) = (p.stdin, p.stdout, p.stderr)
>
>
>
>
> (child_stdin, child_stdout_and_stderr) = os.popen4(cmd, mode, bufsize)
> ==>
> p = Popen(cmd, shell=True, bufsize=bufsize,
>           stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
> (child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout)
>
>
>
>
>
> Return code handling translates as follows:
>
> pipe = os.popen(cmd, 'w')
> ...
> rc = pipe.close()
> if rc is not None and rc >> 8:
>     print("There were some errors")
> ==>
> process = Popen(cmd, 'w', stdin=PIPE)
> ...
> process.stdin.close()
> if process.wait() != 0:
>     print("There were some errors")
>
>
>
> 17.5.5.6. Replacing functions from the popen2 module
>
> Note
> If the cmd argument to popen2 functions is a string, the command is 
> executed through /bin/sh. If it is a list, the command is directly 
> executed.
>
>
>
> (child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode)
> ==>
> p = Popen("somestring", shell=True, bufsize=bufsize,
>           stdin=PIPE, stdout=PIPE, close_fds=True)
> (child_stdout, child_stdin) = (p.stdout, p.stdin)
>
>
>
> (child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], 
> bufsize, mode)
> ==>
> p = Popen(["mycmd", "myarg"], bufsize=bufsize,
>           stdin=PIPE, stdout=PIPE, close_fds=True)
> (child_stdout, child_stdin) = (p.stdout, p.stdin)
>
>
> popen2.Popen3 and popen2.Popen4 basically work as subprocess.Popen, 
> except that:
>     Popen raises an exception if the execution fails.
>     the capturestderr argument is replaced with the stderr argument.
>     stdin=PIPE and stdout=PIPE must be specified.
>     popen2 closes all file descriptors by default,
>     but you have to specify close_fds=True with Popen
>     to guarantee this behavior on all platforms or past Python versions.
> #############################################################
>
> Which bits of that don't you understand?
> That way we have something concrete to work with.
>
> For example, Your popen program:
>
> import os
> pr = os.popen("lpr", "w")
> pr.write(month), pr.write(" "),
> pr.write("\t\tLine ")
>
> Translates according to the above as
>
> import subprocess as sub
> pr = sub.Popen(["lpr"], stdin = sub.PIPE)
> pr.stdin.write(month)
> pr.stdin.write(" ")
> pr.stdin.close()
> if pr.wait() != 0: print 'Errors!'
>
> Now, how can we help further clarify things?
>
Thank for the translation of the hard-to-read docs. Reading the docs 
threw me for a loop. I printed out your response and will be studying to 
try best understand it.

Ken