cpu_percent(interval=None) always returns 0 regardless of interval value PYTHON

Question

The code always returns 0.0 values, regardless of interval values.

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

Answer 1

This behaviour is documented:

When interval is 0.0 or None compares process times to system CPU times elapsed since last call, returning immediately. That means the first time this is called it will return a meaningless 0.0 value which you are supposed to ignore. In this case is recommended for accuracy that this function be called a second time with at least 0.1 seconds between calls.

There is also a warning against using interval=None for a single call:

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

If using interval=None, make sure to call .cpu_percent compared to a prior call.

p = psutil.Process(pid=pid)
p.cpu_percent(interval=None)
for i in range(100):
    usage = p.cpu_percent(interval=None)
    # do other things

instead of:

for i in range(100):
    p = psutil.Process(pid=pid)
    p.cpu_percent(interval=None)
    # do other things

Answer 2

The cpu of a Process object is mutable. I have done some tests for you.

for i in range(10):
    p = psutil.Process(3301)
    print p.cpu_percent(interval=0.1)

result: 9.9 0.0 0.0 0.0 0.0 9.9 0.0 9.9 0.0 0.0

So if you want to get the CPU percent of a Process object, you could take the average in certain time.

test_list = []
for i in range(10):
    p = psutil.Process(6601)
    p_cpu = p.cpu_percent(interval=0.1)
    test_list.append(p_cpu)
print float(sum(test_list))/len(test_list)

result: 1.98