live reloading of small python scripts

livereload.py

"""
    livereload.py - quick "hot reloading" of small python scripts

    demo video: https://imgur.com/a/fLbfHIG
"""

import sys
import os
import time
import traceback

def run(fname, mtime=-1):
    newmtime = os.stat(fname)
    if newmtime == mtime:
        return mtime

    os.system('clear')
    print(f'livereload.py: {fname}\n===========================')

    with open(fname) as f:
        source = f.read()

    try:
        code = compile(source, fname, 'exec')
    except (ValueError, SyntaxError) as e:
        traceback.print_exception(type(e), e, None, file=sys.stdout)
    else:
        d = dict()
        try:
            exec(code, d, d)
        except Exception as e:
            tb = sys.exc_info()[2]
            l = traceback.format_tb(tb)
            print("Traceback (most recent call last):")
            print(*l[1:], end='')
            print(e.__class__.__name__ + ": " + str(e))
    finally:
        return newmtime

def mainloop(fname, delay):
    mtime = -1
    while True:
        mtime = run(fname, mtime)
        try:
            time.sleep(delay)
        except KeyboardInterrupt:
            break

def main():
    usage = "usage: livereload.py <filename> [delay=0.5]"
    fname = sys.argv[1] if len(sys.argv) > 1 else sys.exit(usage)
    delay = sys.argv[2] if len(sys.argv) == 3 else 0.5

    mainloop(fname, delay)

if __name__ == "__main__":
    main()