stopwatch for terminal (python)

stopwatch.py

#!/bin/env python3

import argparse
from contextlib import contextmanager
from datetime import datetime
from datetime import timedelta
from select import select
import termios


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('step', metavar='STEP', nargs='?', default='0.1',
            help='time interval in seconds to update display')
    parser.add_argument('-p', '--precision', metavar='PRECISION', type=int,
            help='how many decimal places to show in seconds, defaults to the number in STEP')

    args = parser.parse_args()
    precision = args.precision
    if precision is None:
        precision = precision_of(args.step)

    stopwatch(float(args.step), precision)


def stopwatch(step, precision):
    # timedelta formats with microseconds, we want to trim any excess decimals
    prec_pos = -6+precision
    if prec_pos == -6:
        prec_pos = -7
    fmt = lambda s: str(s)[:prec_pos]

    # format is fixed width, so don't worry about clear to EOL
    t0 = datetime.now()
    with no_icanon_no_echo():
        while True:
            print(f'\r{fmt(datetime.now()-t0)}', end='')
            r,_,x = select([0], [], [0], step)
            if r or x:
                break
    print(f'\r{fmt(datetime.now()-t0)}')


def precision_of(f):
    # try to determine how much precision was specified after the decimal
    if isinstance(f, str):
        s = f
    else:
        s = f'{f:10f}'.rstrip('0')
    if '.' in s:
        return len(s.split('.', 1)[1])
    return 0


@contextmanager
def no_icanon_no_echo(fd=0):
    iflag, oflag, cflag, lflag, ispeed, ospeed, cc = termios.tcgetattr(fd)
    termios.tcsetattr(fd, termios.TCSANOW, [
        iflag,
        oflag,
        cflag,
        lflag & ~termios.ICANON & ~termios.ECHO,
        ispeed,
        ospeed,
        cc])
    try:
        yield
    finally:
        termios.tcflush(fd, termios.TCIFLUSH)
        termios.tcsetattr(fd, termios.TCSANOW, [
            iflag,
            oflag,
            cflag,
            lflag,
            ispeed,
            ospeed,
            cc])


if __name__ == '__main__':
    main()

Neat. Free lap-counter mode:

while true; do { ./stopwatch.py 0.01; } done