A quick and dirty Python script that writes to a file how long it's been running. Useful for measuring laptop lifetime when on battery (which is what I used it for)

laptop_uptime.py

from time import sleep
from datetime import datetime

"""
To read back JSON file:
Datetime str format: %Y-%m-%d %H:%M:%S.%f
datetime.strptime(datetime_string, "%Y-%m-%d %H:%M:%S.%f")
"""

SLEEP_TIME = 3


def write_time(life_file):
    start_time = datetime.now()
    curr_time = start_time

    time_data = {
        "start": str(start_time),
        "current": None,
        "delta": None
    }

    while True:
        prev_time = curr_time
        curr_time = datetime.now()
        delta = curr_time - start_time
        time_data["current"] = str(curr_time)
        time_data["delta"] = str(delta)

        if (curr_time - prev_time).seconds > SLEEP_TIME * 1.5:
            print(f"""\nABORTING! Skipped ahead more than {SLEEP_TIME} seconds\n
start: {start_time}
end:   {prev_time}
delta: {prev_time - start_time}\n""")
            input("Press enter to continue")
            return

        life_file.seek(0)
        life_file.write(f"""{{
    "start":   "{time_data["start"]}",
    "current": "{time_data["current"]}",
    "delta":   "{time_data["delta"]}"
}}""")
        life_file.truncate()
        life_file.flush()

        print(time_data["delta"])
        sleep(SLEEP_TIME)

def main():
    life_file = open("battery_life.json", "w")

    try:
        write_time(life_file)
    except KeyboardInterrupt:
        return
    finally:
        life_file.close()

if __name__ == "__main__":
    main()