printing out the contents aftre subprocess.call()

[Rakshan]

I am facing a scenario where in I need to execute a jar based on user parameters. I have replicated the scenario here as below :

import subprocess

a = input('Enter either 2 or 3:')

value = int(a)
if a == 2:
    p1 = subprocess.run(['java', '-jar', 'SimpleClient.jar', '-info'], capture_output=True)
    print(p1.stdout.decode())

else:
    p1 = subprocess.run(['java', '-jar', 'SimpleClient.jar'], capture_output=True)
    print(p1.stdout.decode())


print('-----------stdout---------------------')



print('-----------code---------------------')
print(p1.returncode)

What I observe is that the print function does not execute. I expect it to show different results based on my entry.

Error:
Enter either 2 or 3: 2

-----------stdout---------------------
-----------code---------------------
0

I had a doubt if p1 is only within the if and else scope. I put the print stattements even inside those clauses. But that does not help either.

Could anyone guide me here?

[bowlofred]

The order of the things you're printing is odd (you print the separators back to back, while the output is printed before them), but otherwise seems reasonable.

My first thought would be that the program is not producing anything on stdout. Maybe it is all going to stderr or some other location. You can test this by replacing it with something that you know has stdout. When I did that, it printed just fine (albeit before the stdout separator).

[Rakshan]

The order of the things you're printing is odd (you print the separators back to back, while the output is printed before them), but otherwise seems reasonable.

My first thought would be that the program is not producing anything on stdout. Maybe it is all going to stderr or some other location. You can test this by replacing it with something that you know has stdout. When I did that, it printed just fine (albeit before the stdout separator).

yes you are right. It is captured udnder std.err
I am confused here as in, the log messages from the jar which are of type INFO are also a part of the err attribute..
Any reason for that?

[DeaD_EyE]

Maybe the java-program does not write to stdout.
Print also the stderr from the process.

If you put encoding="utf8" in the function call subprocess.run, you don't need to decode the raw bytes, then the function does it for you.
Use functions, to avoid code repetition.


Example:

#!/usr/bin/env python3
"""
Source for test.jar:
http://www.java2s.com/Code/Jar/t/Downloadtestjar.htm
"""

import subprocess


def get_int(question, allowed_values):
    while True:

        print("Please choose from", allowed_values)
        answer = input(question + ": ")

        try:
            value = int(answer)
        except ValueError:
            print("Input is not an integer")
            continue

        if value not in allowed_values:
            print(value, "is not in allowed_values")
            continue

        return value


def run_simple_client(info=False, cwd=None):
    cmd = ["java", "-jar", "test.jar"]

    if info:
        cmd.append("-info")

    return subprocess.run(cmd, capture_output=True, encoding="utf8", cwd=cwd)


def main():
    choices = (1, 2)
    choice = get_int("Please enter your choice", choices)
    print()

    if choice == 1:
        print("Without info")
        proc = run_simple_client()

    # could be an else-block, but maybe you want to extend the menu ...
    elif choice == 2:
        print("With info")
        proc = run_simple_client(info=True)

    print("stdout: ", proc.stdout.rstrip())
    print("stderr: ", proc.stderr.rstrip())
    print("returncode: ", proc.returncode)


if __name__ == "__main__":
    main()

Output:
[andre@andre-Fujitsu-i5 ~]$ LANG=C ./jj.py 
Please choose from (1, 2)
Please enter your choice: 1

Without info
stdout:  
stderr:  no main manifest attribute, in test.jar
returncode:  1

Docs:

• https://docs.python.org/3/tutorial/contr...-functions
  
• https://docs.python.org/3/tutorial/contr...s-on-loops
  
• https://docs.python.org/3/tutorial/error...exceptions
  
• https://docs.python.org/3/tutorial/datas...e-on-lists
  
• https://docs.python.org/3/library/subpro...rocess.run