Time your progress on a monotonous task, print your ETA

slave-timer.py

import sys
import click
import shelve
import datetime
from prompt_toolkit.validation import Validator, ValidationError
from prompt_toolkit import prompt

class NumberValidator(Validator):
    def validate(self, document):
        text = document.text
        if text and not text.isdigit():
            raise ValidationError(message='enter current line number')

def print_stats(records, length):
    alpha, omega = records[0], records[-1]
    time_per_line = ((omega['ts']-alpha['ts']) / (omega['line'] - alpha['line']))
    print("Time per line:", time_per_line)
    print("ETA: ", datetime.datetime.now() + time_per_line * (length - records[-1]['line']))

@click.command()
@click.argument('sheet')
@click.argument('length', type=int)
def main(sheet, length):
    shv = shelve.open("slave-time.shv")
    records = []
    if sheet in shv:
        records = shv[sheet]
    if len(records) > 1:
        print_stats(records, length)
        print("Last record:", records[-1])
    while True:
        line = int(prompt('Line: ', validator=NumberValidator()))
        records.append(dict(line=line, ts=datetime.datetime.now()))
        shv[sheet] = records
        if len(records) > 1:
            print_stats(records, length)


if __name__ == '__main__':
    main()