casts.py

"""
Provides a cast operations module.

>>> cast_to_decimal(1.0001)
Decimal('1.0001')
>>> cast_to_decimal(1)
Decimal('1')
>>> cast_to_decimal("1.0001")
Decimal('1.0001')
>>> cast_to_decimal(Decimal("1.0001"))
Decimal('1.0001')

>>> cast_to_date("2015-01-01")
date(2015, 1, 1)
>>> cast_to_date(datetime.now()) == date.today()
True
>>> cast_to_date(date(2015, 1, 1))
date(2015, 1, 1)
"""

from decimal import Decimal

from datetime import date, datetime
from multimethod import multidispatch


@multidispatch
def cast_to_decimal(arg):
    """
    Casts the given argument to Decimal, if possible. Raises ValueError
    if argument is not recognized as compatible.

    :param arg: The argument to be cast to Decimal.
    :return: A Decimal or raises a ValueError
    """
    raise ValueError("{} can not be cast to Decimal".format(repr(arg)))


@cast_to_decimal.register(float)
def _(arg):
    return Decimal(str(arg))


@cast_to_decimal.register(int)
def _(arg):
    return Decimal(arg)


@cast_to_decimal.register(str)
def _(arg):
    return Decimal(arg)


@cast_to_decimal.register(Decimal)
def _(arg):
    return arg


@multidispatch
def cast_to_date(arg):
    """
    Casts the given argument to date, if possible. Raises ValueError
    if argument is not recognized as compatible.

    :param arg: The argument to be cast to date.
    :return: A date or raises a ValueError
    """
    raise ValueError("{} can not be cast to date".format(repr(arg)))


@cast_to_date.register(str)
def _(arg):
    return datetime.strptime(arg, "%Y-%m-%s")


@cast_to_date.register(datetime)
def _(arg):
    return datetime.date()


@cast_to_date.register(date)
def _(arg):
    return arg