Compute per-diem for travel based on GSA M&IE (Meals and Incidental Expenses)

perdiem.py

#!/usr/bin/env python3

import argparse

from tabulate import tabulate
from datetime import datetime, timedelta


DATE_FMT = "%Y-%m-%d"
ONE_DAY = timedelta(days=1)


def main(args):
    start = datetime.strptime(args.start, DATE_FMT)
    end = datetime.strptime(args.end, DATE_FMT)

    mie = args.rate
    travel = 0.75*mie

    # Show the detail of the computation
    if args.detail:
        table = []
        total = 0.0

        day = start
        while day != end:
            if day == start:
                table.append([day.date(), travel])
                total += travel
            else:
                table.append([day.date(), mie])
                total += mie

            day += ONE_DAY

        # Handle the last day
        total += travel
        table.append([day.date(), travel])

        table.append(["total", total])
        print(tabulate(table))
        return

    # Otherwise just do the computation
    # Compute number of days in the trip inclusive of the start and end date
    days = (end - start).days + 1

    if days == 1:
        print(f"the per diem for one day is ${travel:0.2f}")
    elif days == 2:
        rate = travel*2
        print(f"the per diem for two days is ${rate:0.2f}")
    else:
        rate = (2*travel) + ((days-2)*mie)
        print(f"the per diem for {days} days is ${rate:0.2f}")


if __name__ == "__main__":
    args = {
        ("-s", "--start"): {
            "type": str, "metavar": "YYYY-MM-DD", "required": True,
            "help": "start date of the trip to compute MI&E for",
        },
        ("-e", "--end"): {
            "type": str, "metavar": "YYYY-MM-DD", "required": True,
            "help": "end date of the trip to compute MI&E for",
        },
        ("-r", "--rate"): {
            "type": float, "metavar": "DD.CC", "required": True,
            "help": "the MI&E rate from gsa.gov",
        },
        ("-d", "--detail"): {
            "action": "store_true", "default": False,
            "help": "print out a detail of the rate per day"
        },
    }

    parser = argparse.ArgumentParser(
        description="compute MI&E per-diem for a specified date range",
        epilog="the per-diem rate must be looked up on gsa.gov",
    )

    for pargs, kwargs in args.items():
        if isinstance(pargs, str):
            pargs = (pargs,)
        parser.add_argument(*pargs, **kwargs)

    args = parser.parse_args()
    main(args)