Rates calculator

ralc.py

#!/usr/bin/env python
#
# Rates calculator.
#
# Requirements
# ============
#
# * `Python <http://www.python.org/>`_ 2.7
#
# Installation
# ============
#
# * Save ``ralc`` script somewhere in your ``$PATH``, in most cases ``~/bin``
#   would be enough.
# * Give the execution rights to this script, ``chmod +x ~/bin/ralc``
#
# Usage
# =====
#
# ::
#
#     $ ralc HH[:MM[:SS]] RATE
#

import sys

from decimal import Decimal, ROUND_UP


__author__ = 'Igor Davydenko'
__license__ = 'BSD License'
__script__ = 'ralc'
__version__ = '0.1'


def main():
    """
    Make calculations if all arguments passed properly.
    """
    if len(sys.argv) != 3:
        usage()

    _, delta, rate = sys.argv
    hours, minutes, seconds = 0, 0, 0

    if not ':' in delta:
        hours = delta
    elif delta.count(':') == 1:
        hours, minutes = delta.split(':')
    elif delta.count(':') == 2:
        hours, minutes, seconds = delta.split(':')
    else:
        print >> sys.stderr, 'ERROR: Invalid value for hours, please use ' \
                             'next format, HH[:MM[:SS]]. Exit..'
        sys.exit(1)

    hours = to_int(hours, 'hours')
    minutes = to_int(minutes, 'minutes')
    seconds = to_int(seconds, 'seconds')
    rate = to_decimal(rate, 'rate')

    remainder = Decimal(minutes * 60 + seconds) / Decimal(3600)
    remainder = remainder.quantize(Decimal('.01'), ROUND_UP)
    value = Decimal(hours) + remainder
    result = (value * rate).quantize(Decimal('.01'), ROUND_UP)

    print('> {} x {} = {}'.format(value, rate, result))


def to_decimal(value, label):
    """
    Try to convert value to decimal and exit if fails.
    """
    try:
        return Decimal(value)
    except (TypeError, ValueError):
        print >> sys.stderr, 'ERROR: Cannot convert {}, {!r}, to decimal. ' \
                             'Exit...'.format(label, value)
        sys.exit(1)


def to_int(value, label):
    """
    Try to convert value to integer and exit if fails.
    """
    try:
        return int(value)
    except (TypeError, ValueError):
        print >> sys.stderr, 'ERROR: Cannot convert {}, {!r}, to integer. ' \
                             'Exit...'.format(label, value)
        sys.exit(1)


def usage():
    """
    Print usage message to stderr and exit.
    """
    print >> sys.stderr, 'Usage: {} HH[:MM[:SS]] RATE'.format(__script__)
    sys.exit(1)


if __name__ == '__main__':
    main()