Retrieve the Outputs from subprocess.Popen

Gordon1998

Hi, everyone.

I have read that there are some discussions about using the subprocess.Popen() or subprocess.run() module to run CPython code. I have managed to call functions written in CPython by subprocess modules to make the plots. However, I have trouble retrieving the outputs from Cpython. Normally, subprocess.Popen() can use the pipeline to return outputs and error codes. But this is not working with ANSYS IronPython. Can someone shed some light on reading outputs from Cpython functions? I am using the latest ANSYS 2024R2.

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Accepted answers

Rajesh Meena

Hi @Gordon1998 ,

@Gordon1998

I do not think you have shared with me the working script. The shared script will not work in CPython and IronPython.

But here is what I am trying, both in CPython and IronPython.

I have two scripts:

add_times.py having below content:

import sys
def add_times(a, b):
    c = a + b
    d = a * b
    return c, d

if __name__=='__main__':
    print(add_times(float(sys.argv[1]),float(sys.argv[2])))

subprocess_test.py

import subprocess

a = 1
b = 2
process = subprocess.Popen([r"D:\Workshop\demo\demo_crng_env\Scripts\python.exe","D:/add_times.py", 
                 str(a), str(b)],
                 stdout=subprocess.PIPE, 
                 stderr=subprocess.PIPE)


stdout, stderr = process.stdout.read(), process.stderr.read()

print("Output:", stdout)
print("Error:", stderr if stderr else "No error")

Below are the outputs:

From IronPython in mechanical:

From CPython in VSCode:

All comments

Rajesh Meena

Does this help?

`
import subprocess

Define the command you want to run

command = [r"C:/Users/56577474/.ansys_python_venvs/pygeom_2511/Scripts/python.exe", "-m","pip","list"]

Start the subprocess and capture the output

process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

Read the output and error

stdout, stderr = process.stdout.read(), process.stderr.read()

print("Output:", stdout)
print("Error:", stderr if stderr else "No error")

Gordon1998

@Rajesh Meena said:
Does this help?

`
import subprocess

Define the command you want to run

command = [r"C:/Users/56577474/.ansys_python_venvs/pygeom_2511/Scripts/python.exe", "-m","pip","list"]

Start the subprocess and capture the output

process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

Read the output and error

stdout, stderr = process.stdout.read(), process.stderr.read()

print("Output:", stdout)
print("Error:", stderr if stderr else "No error")

`

Hi, Rajesh. Thanks for your reply. I have tried this method before. However, the IronPython adopted by ANSYS ACT is quite old. It does not have a subprocess.PIPE feature. If you run the code, you will realize that stdout reads nothing from the subprocess. But if you run this in Cpython, this code will work.

Rajesh Meena

@Gordon1998 I tried this in Ansys 2024R2 mechanical scripting console and it worked fine. I got a list of modules installed in that particular python environment via subprocess.

How are you running IronPython script?

Gordon1998

Hi Rajesh, thanks for your reply. I have tried your scripts before. Let's say we have a simple function that is stored in a separate file called 'add_times.py' as shown below:

def add_times(a, b):
    c = a + b
    d = a * b
    return c, d

I call this function from the 'main.py' as:

a = 1
b = 2
subprocess.Popen("python","add_times.py", 
                 str(a), str(b),
                 stdout=subprocess.PIPE, 
                 stderr=subprocess.PIPE)

If I deploy this code into ANSYS ACT, both 'stdout' and 'stderr' will return 'None'. However, if I deploy the same code in VSCode (I use Cpython), this code can return the outputs. So I am afraid that 'subprocess.PIPE' is not implemented in ANSYS ACT (IronPython).

Rajesh Meena

Hi @Gordon1998 ,

@Gordon1998

I do not think you have shared with me the working script. The shared script will not work in CPython and IronPython.

But here is what I am trying, both in CPython and IronPython.

I have two scripts:

add_times.py having below content:

import sys
def add_times(a, b):
    c = a + b
    d = a * b
    return c, d

if __name__=='__main__':
    print(add_times(float(sys.argv[1]),float(sys.argv[2])))

subprocess_test.py

import subprocess

a = 1
b = 2
process = subprocess.Popen([r"D:\Workshop\demo\demo_crng_env\Scripts\python.exe","D:/add_times.py", 
                 str(a), str(b)],
                 stdout=subprocess.PIPE, 
                 stderr=subprocess.PIPE)


stdout, stderr = process.stdout.read(), process.stderr.read()

print("Output:", stdout)
print("Error:", stderr if stderr else "No error")

Below are the outputs:

From IronPython in mechanical:

From CPython in VSCode:

Gordon1998

Hi, Rajesh. This works on my computer! Thank you so much.

Rajesh Meena

@Gordon1998

Great! I have selected my last response as the answer to this post.