[Tutor] Issue in using "subprocess.Popen" for parsing the command output
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
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,
___
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Issue in using "subprocess.Popen" for parsing the command output
Even only with "*proc.decode("utf-8")"* in the above code still it seems to
throw the error
#return proc.strip().decode("utf-8")
#return proc.decode("utf-8").strip()
*return proc.decode("utf-8")*
Error:
/home/srinivasan/Downloads/wifidisconnectissuenov23_homework/venv/bin/python
/home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py
printing stdout!!
printing retcode!! 0
Traceback (most recent call last):
File
"/home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py",
line 31, in
main("Apartment 18", "40672958689850014685")
* File
"/home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py",
line 29, in main*
*return proc.decode("utf-8")*
*AttributeError: 'Popen' object has no attribute 'decode'*
Process finished with exit code 1
On Sun, Nov 25, 2018 at 11:24 PM srinivasan
wrote:
> Hope now I have changed on the string output as below, could you please
> correct me if am still wrong?
>
> import sys
> import subprocess
>
> interface = "wlan0"
>
>
> def main(ssid, pw):
>
> 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=True)
> raise AssertionError(s)
>
> #return proc.strip().decode("utf-8")
> *return proc.decode("utf-8").strip()*
>
> main("Apartment 18", "40672958689850014685ad")
>
> Error:
>
> /home/srinivasan/Downloads/wifidisconnectissuenov23_homework/venv/bin/python
> /home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py
> Traceback (most recent call last):
> File
> "/home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py",
> line 30, in
> main("Apartment 18", "40672958689850014685")
> * File
> "/home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py",
> line 28, in main*
> *return proc.decode("utf-8").strip()*
> *AttributeError: 'Popen' object has no attribute 'decode'*
> printing stdout!!
> printing retcode!! 0
>
> Process finished with exit code 1
>
>
>
> On Sun, Nov 25, 2018 at 11:19 PM MRAB wrote:
>
>> 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)*
>> > *s
Re: [Tutor] Issue in using "subprocess.Popen" for parsing the command output
On 11/25/18 10:58 AM, srinivasan wrote:
> Even only with "*proc.decode("utf-8")"* in the above code still it seems to
> throw the error
>
> #return proc.strip().decode("utf-8")
> #return proc.decode("utf-8").strip()
> *return proc.decode("utf-8")*
>
> Error:
> /home/srinivasan/Downloads/wifidisconnectissuenov23_homework/venv/bin/python
> /home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py
> printing stdout!!
> printing retcode!! 0
> Traceback (most recent call last):
> File
> "/home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py",
> line 31, in
> main("Apartment 18", "40672958689850014685")
> * File
> "/home/srinivasan/Downloads/wifidisconnectissuenov23_homework/qa/test_library/test4.py",
> line 29, in main*
> *return proc.decode("utf-8")*
> *AttributeError: 'Popen' object has no attribute 'decode'*
the error tells you what is wrong. proc is a Popen object, and does not
have a decode method. simple enough. strings have a decode method.
You're decoding the wrong thing, you need to decode what you get back
from communicating with the Popen object, not the Popen object itself.
stdin is the string (or more likely, in Python 3, a bytes object) you
got back from calling communicate(). decode that.
___
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Issue in using "subprocess.Popen" for parsing the command output
I think you are sending email using Gmail. If so, there is a command in
Gmail to send only PLAIN TEXT with no added formatting. Please use it.
Your code at the moment has extra asterisks * added at the beginning and
end of each line.
More comments below.
On Sun, Nov 25, 2018 at 10:43:10PM +0530, srinivasan wrote:
> 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.
As a beginner, you should normally not use try...except to report
errors. You should learn how to diagnose errors by reading the
traceback. Covering up the traceback with try...except makes debugging
harder.
Your use here:
> *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)*
doesn't seem right to me. The string.format() method doesn't take a
shell=enable_shell agument, so I expect that line
s = """...""".format(cmd, ..., shell=enable_shell)
to fail. But even if it doesn't fail, the next line:
raise AssertionError(s)
is an abuse of exceptions. The failure here is *not* an assertion, and
you shouldn't use AssertionError. You wouldn't use TypeError or
UnicodeEncodeError or AttributeError. "AssertionError" should not be
used for "some arbitrary error".
There are almost no reasons to manually raise AssertionError, except
perhaps in test frameworks like unittest. Normally you should only get
an AssertionError from the "assert" command:
https://import-that.dreamwidth.org/676.html
My opinion is, you should remove that try...except altogether. I don't
think that it helps your code, even if it worked. Calls to Popen can
fail in many, many ways, and it seems pointless to single out just one
of them and to replace the useful traceback and error message with a
less accurate one.
> *Command:*
> :~$ nmcli device wifi connect 'Apartment 18' password
> '40672958689850014685abcdf'
> Error: Connection activation failed: (7) Secrets were required, but not
> provided.
If you cannot get nmcli working directly from the command line, you have
*no hope* of getting it working with Python getting in the way.
*First* you must be able to run the command directly from the shell,
with no errors. Then you can move the *working* command to Python and
Popen.
> return proc.strip().decode("utf-8")
> AttributeError: 'Popen' object has no attribute 'strip'
The error should explain exactly what the problem is. You are tying to
call the STRING METHOD string.decode on a Popen object. Did you read the
error message?
I don't know how to fix it because I don't know what you are trying to
do.
--
Steve
___
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Issue in using "subprocess.Popen" for parsing the command output
On 26Nov2018 09:03, Steven D'Aprano wrote:
On Sun, Nov 25, 2018 at 10:43:10PM +0530, srinivasan wrote:
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.
As a beginner, you should normally not use try...except to report
errors. You should learn how to diagnose errors by reading the
traceback. Covering up the traceback with try...except makes debugging
harder.
Very true, but...
Your use here:
*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)*
[...]
But even if it doesn't fail, the next line:
raise AssertionError(s)
is an abuse of exceptions. The failure here is *not* an assertion, and
you shouldn't use AssertionError. You wouldn't use TypeError or
UnicodeEncodeError or AttributeError. "AssertionError" should not be
used for "some arbitrary error". [...]
My opinion is, you should remove that try...except altogether. I don't
think that it helps your code, even if it worked. Calls to Popen can
fail in many, many ways, and it seems pointless to single out just one
of them and to replace the useful traceback and error message with a
less accurate one.
I'd add one qualificaion here: it may be that he wants to report this
exception in particular, while still not "handling it". In which case
I'd advocate something like:
try:
... Popen stuff ...
except subprocess.CalledProcessError as e:
s =
print(s, file=sys.stderr)
raise
i.e. report some special message, then _reraise_ the original exception.
In this way he gets to keep the original exception and traceback for
debugging, which still making whatever special message he wanted to
make.
Cheers,
Cameron Simpson
___
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A required question
On Sat, Nov 24, 2018, 14:33 Avi Gross David, > > As I suspected. Yes, I am aware how to do those things. Just wondered if > anyone automated the process so a fairly simple interface worked. > Does the requirements.txt file (associated with pip IIRC) does most of what you want? > > I am dropping the request. > > Avi > > -Original Message- > From: Tutor On Behalf Of > David Rock > Sent: Friday, November 23, 2018 9:28 PM > To: Tutor Python > Subject: Re: [Tutor] A required question > > > > On Nov 23, 2018, at 09:35, Alan Gauld via Tutor > wrote: > > > > On 23/11/2018 05:34, Avi Gross wrote: > >> What I was thinking was the ability to do something like this: > >> > >> import ReChoir as require > >> > >> require.version(condition, before=True, after=False) > >> require.modules(module list, recursive=True) require.os([“Eunuchs”, > >> “Windblows”]) > >> require.functionality(“print3”) > > > > I can see the logic but suspect discussion of new features is probably > > the preserve of the main Python list. If you can get traction there > > somebody might actually go ahead and write one! > > discussion of a “require” library probably isn’t necessary. It’s pretty > straightforward to include the logic using existing methods. > > For the version of python, test against sys.version_info For the modules, > put your import calls in a try block and handle exceptions For the OS > version, test against os.name or sys.platform The last one, > “functionality,” is a bit vague. Probably another candidate for a try > block. > > > — > David Rock > da...@graniteweb.com > > > > > ___ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > https://mail.python.org/mailman/listinfo/tutor > > ___ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > https://mail.python.org/mailman/listinfo/tutor > ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
