[RPi OS] Invalid CPU percentage values

[hex-developer]

Summary

• OS: Raspberry Pi OS Lite
• Architecture: ARM
• Psutil version: 5.8.0
• Python version: Python 3.9.2
• Type: not sure

Description

I am using psutil to return cpu usage for each core. From the python interpreter this works correctly, however from a script it does not.
Both are using the same python version.
The code I run is

import psutil
print(psutil.cpu_percent(percpu=True))

In both cases, this returns no errors.
When executing the script, I get values such as [0.0, 0.0, 0.0, 0.0] and [0.0, 0.0, 100.0, 0.0]
Running htop proves that cpu usage is different and that all cores are used.
Even rebooting failed to help.

[hex-developer]

I upgraded to psutil version 5.9.4 and I still have the same results

[giampaolo]

From doc:

Warning: the first time this function (psutil.cpu_percent()) is called with interval = 0.0 or None it will return a meaningless 0.0 value which you are supposed to ignore.

Translated: to get meaningful values you have to call psutil.cpu_percent() in a loop with an interval:

while 1:
    print(psutil.cpu_percent())
    time.sleep(1)

[hex-developer]

I wrote the same code in a different way and it worked. Thank you!