cpu_percent return 0.0 for single process, but it was okay for system-wild CPU utilization

[mozz85]

Summary

psutil 5.9.2
windows

Description

here is the test code

import subprocess
import psutil
import time

os_process = subprocess.Popen('notepad', stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
psutil_process = psutil.Process(os_process.pid)
time.sleep(1)
print(psutil_process.cpu_percent(interval=None))
time.sleep(1)
print(psutil_process.cpu_percent(interval=None))
time.sleep(1)
print(psutil_process.cpu_percent(interval=None))
time.sleep(1)
print(psutil_process.cpu_percent(interval=None))

here is the output

if the image load failed
0.0
0.0
0.0
0.0

[mozz85]

i can get the vaild value of system-wild CPU utilization

time.sleep(1)
print(psutil.cpu_percent(interval=None))
time.sleep(1)
print(psutil.cpu_percent(interval=None))
time.sleep(1)
print(psutil.cpu_percent(interval=None))
time.sleep(1)
print(psutil.cpu_percent(interval=None))

output goes like
4.7
2.5
5.5
3.6

i also tried for the current process like this, and i failed too

p = psutil.Process()
time.sleep(1)
print(p.cpu_percent(interval=None))
time.sleep(1)
print(p.cpu_percent(interval=None))
time.sleep(1)
print(p.cpu_percent(interval=None))
time.sleep(1)
print(p.cpu_percent(interval=None))

output goes like
0.0
0.0
0.0
0.0

[mozz85]

[giampaolo]

I guess it's because the process does basically nothing.

[mozz85]

You are right. Althought the process that i want to check out did something, when i print out the os_process.pid, i found out that's not it. The code that i copied from chatgpt set the shell=True when calling the Popen. and i know nothing about it. That opens a shell, and that shell opens the intended process.