#!/usr/bin/env python3

from time import sleep, time

import os

from sys import stdout, stderr

psi_path = '/proc/pressure/memory'

psi_support = os.path.exists(psi_path)


def rline1(path):
    """read 1st line from path."""
    with open(path) as f:
        for line in f:
            return line[:-1]


def psi_mem_some_avg_total():
    return float(rline1(psi_path).rpartition('=')[2])

avg_min_time = 0.1

if psi_support:
    ta0 = time()
    a0 = psi_mem_some_avg_total()


while True:

    if psi_support:

        ta1= time()
        dt = ta1 - ta0

        if dt >= avg_min_time:

            a1 = psi_mem_some_avg_total()
            avg = (a1 - a0) / (ta1 - ta0) / 100

            print('PSI mem avg:', round(avg, 2))
            ta0 = ta1
            a0 = a1

    stdout.flush()
    sleep(1)