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Issue in using "subprocess.Popen" for parsing the command output


On 2018-11-25 17:13, srinivasan wrote:
> Dear Python Experts Team,
> 
> As am newbie still learning the python syntax from past 2 weeks, Excuse me,
> If this might be silly question, As I am trying to execute shell command
> (ie, nmcli) using "subprocess.Popen".
> 
> 1. Am trying to improve the below code with "try" and "exception", could
> you please help me how "try" and "exception" can be used on the below code
> snippet. I hope in my code with try and exception, seems to be a bug.
> 
> 2. As I am trying to execute shell commands using "subprocess.Popen", I am
> trying to parse the strings output by "cmd = "nmcli device wifi connect
> '%s' password '%s'" % (ssid, pw)" command as below, but it is throwing the
> below error as shown in "Output error logs:"
> 
>   Could you please let me to fix the bug in the below code snippet, where I
> need the collect the strings of the command output and later how to be
> parsed after execution of the command for example, I need to parse the
> string "Connection activation failed: " and compare it with the command
> output, could you please help me how this can be achieved?
> 
> *Command:*
> :~$ nmcli device wifi connect 'Apartment 18' password
> '40672958689850014685abcdf'
> Error: Connection activation failed: (7) Secrets were required, but not
> provided.
> :~$
> 
> *Code:*
> *import sys*
> *import subprocess*
> 
> *interface = "wlan0"*
> 
> 
> *def main(ssid, pw):*
> 
> *    # cmd = "nmcli device wifi connect '%s' password '%s'" % (ssid, pw)*
> *    #*
> *    # proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,
> stderr=subprocess.PIPE, shell=True,  universal_newlines=True)*
> *    # stdout, stderr = proc.communicate()*
> *    # retcode = proc.returncode*
> *    #*
> *    # print("printing stdout!!!!!!!!!!", stdout)*
> *    # print("printing retcode!!!!!!!!!!", retcode)*
> 
> *    try:*
> *        cmd = "nmcli device wifi connect '%s' password '%s'" % (ssid, pw)*
> 
> *        proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,
> stderr=subprocess.PIPE, shell=True, universal_newlines=True)*
> *        stdout, stderr = proc.communicate()*
> *        retcode = proc.returncode*
> 
> *        print("printing stdout!!!!!!!!!!", stdout)*
> *        print("printing retcode!!!!!!!!!!", retcode)*
> 
> *    except subprocess.CalledProcessError as e:*
> *        s = """While executing '{}' something went wrong.*
> *                        Return code == '{}'*
> *                        Return output:\n'{}'*
> *                        """.format(cmd, e.returncode, e.output,
> shell=enable_shell)*
> *        raise AssertionError(s)*
> 
> *    return proc.strip().decode("utf-8")*
> 
> *main("Apartment 18", "40672958689850014685")*
> 
> *Output error logs:*
> 
> /home/srinivasan/Downloads/wifidisconnectissuenov23/qa/venv/bin/python
> /home/srinivasan/Downloads/wifidisconnectissuenov23/qa/test_library/test4.py
> Traceback (most recent call last):
>    File
> "/home/srinivasan/Downloads/wifidisconnectissuenov23/qa/test_library/test4.py",
> line 38, in <module>
> printing stdout!!!!!!!!!!
> printing retcode!!!!!!!!!! 0
>      main("Apartment 18", "40672958689850014685")
>    File
> "/home/srinivasan/Downloads/wifidisconnectissuenov23/qa/test_library/test4.py",
> line 36, in main
>      return proc.strip().decode("utf-8")
> AttributeError: 'Popen' object has no attribute 'strip'
> 
> Process finished with exit code 1
> 
> Kindly do the needful as am stuck with this issue from 2 days
> 
> Many Thanks in advance,
> 
Look carefully at the traceback. It's actually telling you what the 
problem is.

You're trying to do .strip() on proc, but proc is the process itself.

Instead, what you want is to do .strip() on the string that it output.