problem in using subprocess module

[akbarza]

hi
when i was reading the page https://realpython.com/python-eval-funct...es-of-eval about eval() in python, i encounterd a problem.
in the code (the below code is on the above page):

# Run the echo command
import subprocess
eval("subprocess.getoutput('echo Hello, World')")

# Launch Firefox (if available)
eval("subprocess.getoutput('firefox')")

when I ran it, I took the below :

Error:
"'firefox' is not recognized as an internal or external command,\noperable program or batch file."

I think the code is used for running Firefox from inside Python. is it true?
why did not the code run successfully?
I have another question:
is it possible to take information about something in Python? For example, suppose I want to know about %
usage in Python. when I am in idle , I wrote help(%), and it takes an error as

Error:
SyntaxError: invalid syntax

. how can I take information about something in idle?
thanks

[snippsat]

I think the code is used for running Firefox from inside Python. is it true?
why did not the code run successfully?

Yes it will try to run the FireFox binary,but i think you misunderstand how this work.
As the Firefox(Browser) is a long running process and may give no output to stdout at all.
The eval make no sense here,can only use Python eval if output make any sense for this and are secure for task like this.

To give example of that make some sense,so eg when run ping on command line,
it give output about request messages to a target Ip.

import subprocess

response = subprocess.run(['ping', '-n' ,'4', 'python-forum.io'], capture_output=True, encoding='utf-8')
print(response.stdout)

Output:
Pinging python-forum.io [2606:4700:3035::6815:1b29] with 32 bytes of data:
Reply from 2606:4700:3035::6815:1b29: time=37ms 
Reply from 2606:4700:3035::6815:1b29: time=26ms 
Reply from 2606:4700:3035::6815:1b29: time=37ms 
Reply from 2606:4700:3035::6815:1b29: time=42ms 

Ping statistics for 2606:4700:3035::6815:1b29:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 26ms, Maximum = 42ms, Average = 35ms

So now in subprocess running the ping command and capture is output.

Also subprocess.getoutput() is not common used at all.

Using the subprocess Module

The recommended approach to invoking subprocesses is to use the run() function for all use cases it can handle.
For more advanced use cases, the underlying Popen interface can be used directly.

[akbarza]

I think the code is used for running Firefox from inside Python. is it true?
why did not the code run successfully?

Yes it will try to run the FireFox binary,but i think you misunderstand how this work.
As the Firefox(Browser) is a long running process and may give no output to stdout at all.
The eval make no sense here,can only use Python eval if output make any sense for this and are secure for task like this.

To give example of that make some sense,so eg when run ping on command line,
it give output about request messages to a target Ip.

import subprocess

response = subprocess.run(['ping', '-n' ,'4', 'python-forum.io'], capture_output=True, encoding='utf-8')
print(response.stdout)

Output:
Pinging python-forum.io [2606:4700:3035::6815:1b29] with 32 bytes of data:
Reply from 2606:4700:3035::6815:1b29: time=37ms 
Reply from 2606:4700:3035::6815:1b29: time=26ms 
Reply from 2606:4700:3035::6815:1b29: time=37ms 
Reply from 2606:4700:3035::6815:1b29: time=42ms 

Ping statistics for 2606:4700:3035::6815:1b29:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 26ms, Maximum = 42ms, Average = 35ms

So now in subprocess running the ping command and capture is output.

Also subprocess.getoutput() is not common used at all.

Using the subprocess Module

The recommended approach to invoking subprocesses is to use the run() function for all use cases it can handle.
For more advanced use cases, the underlying Popen interface can be used directly.

hi snippet
I am not familiar with the subprocess library and your code:

response = subprocess.run(['ping', '-n' ,'4', 'python-forum.io'], capture_output=True, encoding='utf-8')

how(where) can I gain more info about the above code?
do you have any opinion about my second question?
thanks a lot.

[akbarza]

Yes it will try to run the FireFox binary,but i think you misunderstand how this work.
As the Firefox(Browser) is a long running process and may give no output to stdout at all.
The eval make no sense here,can only use Python eval if output make any sense for this and are secure for task like this.

To give example of that make some sense,so eg when run ping on command line,
it give output about request messages to a target Ip.

import subprocess

response = subprocess.run(['ping', '-n' ,'4', 'python-forum.io'], capture_output=True, encoding='utf-8')
print(response.stdout)

Output:
Pinging python-forum.io [2606:4700:3035::6815:1b29] with 32 bytes of data:
Reply from 2606:4700:3035::6815:1b29: time=37ms 
Reply from 2606:4700:3035::6815:1b29: time=26ms 
Reply from 2606:4700:3035::6815:1b29: time=37ms 
Reply from 2606:4700:3035::6815:1b29: time=42ms 

Ping statistics for 2606:4700:3035::6815:1b29:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 26ms, Maximum = 42ms, Average = 35ms

So now in subprocess running the ping command and capture is output.

Also subprocess.getoutput() is not common used at all.

hi snippet
I am not familiar with the subprocess library and your code:

response = subprocess.run(['ping', '-n' ,'4', 'python-forum.io'], capture_output=True, encoding='utf-8')

how(where) can I gain more info about the above code?
do you have any opinion about my second question?
thanks a lot.

hi
I ran your code in idle.
the print line without the stdout statement printed messy but with it, the output is clean.
when must the stdout statement be used?
thanks

[deanhystad]

stdout is a method, not a statement. This is a statement.

print(response.stdout)

The statement calls the print function, passing response.stdout as the argument.

If you read the documentation for subprocess: https://docs.python.org/3/library/subprocess.html

Output:
class subprocess.CompletedProcess
The return value from run(), representing a process that has finished.

args
The arguments used to launch the process. This may be a list or a string.

returncode
Exit status of the child process. Typically, an exit status of 0 indicates that it ran successfully.

A negative value -N indicates that the child was terminated by signal N (POSIX only).

stdout
Captured stdout from the child process. A bytes sequence, or a string if run() was called with an encoding, errors, or text=True. None if stdout was not captured.

If you ran the process with stderr=subprocess.STDOUT, stdout and stderr will be combined in this attribute, and stderr will be None.

response is a CompletedProcess object. response.stdout is the captured stdout from the child process.

Python documentation is pretty good.

[snippsat]

hi snippet
I am not familiar with the subprocess library and your code:

response = subprocess.run(['ping', '-n' ,'4', 'python-forum.io'], capture_output=True, encoding='utf-8')

how(where) can I gain more info about the above code?

To explain the basic of this,so ping is a external program ping.exe that you have on your OS Windows .
From cmd:

C:\>ping -n 4 python-forum.io

Pinging python-forum.io [172.67.168.227] with 32 bytes of data:
Reply from 172.67.168.227: bytes=32 time=21ms TTL=53
Reply from 172.67.168.227: bytes=32 time=37ms TTL=53
Reply from 172.67.168.227: bytes=32 time=32ms TTL=53
Reply from 172.67.168.227: bytes=32 time=35ms TTL=53

Ping statistics for 172.67.168.227:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 21ms, Maximum = 37ms, Average = 31ms 

So it's a way to take a external programs into Python,and run it if program have output can also catch that.
Like this will just start FireFox from Python.

import subprocess

subprocess.run(['C:/Program Files (x86)/Mozilla Firefox/firefox.exe'])

Look at Doc for eg run().