Terminal latency meter

tlatency.py

#!/usr/bin/env python

import math
import time
import curses


def median(lst):
    n = len(lst)
    if n < 1:
        return None
    if n % 2 == 1:
        return sorted(lst)[n//2]
    else:
        return sum(sorted(lst)[n//2-1:n//2+1])/2.0

def main(stdscr):
    curses.curs_set(0)
    stdscr.nodelay(1)
    stdscr.leaveok(1)

    stdscr.addstr(1, 1, "Terminal Latency Meter ----------------------------")
    stdscr.addstr(2, 1, "  - Press spacebar in time with the flashing light")
    stdscr.addstr(3, 1, "  - Press q to exit")
    
    running = True
    key_latencies = []
    key_latency_cut = 0
    while running:
        b = int(time.time()) % 2 and "#" or " "
        for i in range(3):
            stdscr.addstr(10 + i, 20, b * 3)
        display_point = time.time()
        display_latency = (display_point % 1.0) * 1000
        stdscr.addstr(16, 10, "Display latency: %8.3f ms" % display_latency)
        if key_latencies:
            stdscr.addstr(17, 14, "Key latency: %8.3f ms" % key_latencies[-1])
            avg_latency = sum(key_latencies) / len(key_latencies)
            med_latency = median(key_latencies)
            stdscr.addstr(18, 14, "    Average: %8.3f ms" % avg_latency)
            stdscr.addstr(19, 14, "     Median: %8.3f ms" % med_latency)
        stdscr.refresh()
        next_refresh = math.ceil(time.time())
        
        while running:
            if time.time() >= next_refresh:
                break
            
            try:
                c = stdscr.getkey()
            except curses.error:
                c = ''

            if c == 'q':
                running = False
            elif c == 'TIMEOUT':
                break

            if c == ' ' and time.time() > key_latency_cut:
                bright_point = display_point
                if b == ' ':
                    bright_point += 1.0
                key_latencies.append((time.time() - bright_point) * 1000)
                key_latency_cut = time.time() + 1.5
                

curses.wrapper(main)