randdecimal.py

import unittest

from decimal import Decimal
from random import randint


class TestRandDecimal(unittest.TestCase):

    def check(self, a, b):
        value = randdecimal(a, b)
        self.assertTrue(Decimal(a) <= value <= Decimal(b),
                        'not %r <= %r <= %r' % (a, value, b))

    def test_result(self):
        self.check(0, 10)
        self.check('0.13', '0.20')
        self.check(Decimal('5.33'), 10)
        self.check(0, Decimal('5.33'))
        self.check(Decimal('0.135'), Decimal('0.2'))

    def test_same(self):
        self.assertEqual(randdecimal(0, 0), 0)
        self.assertEqual(randdecimal('0.2', '.2'), Decimal('.2'))
        self.assertEqual(randdecimal(10, Decimal('10.00')), Decimal('10'))

    def test_value_error(self):
        self.assertRaises(ValueError, randdecimal, 10, 0)
        self.assertRaises(ValueError, randdecimal, '0.2', '0.135')
        self.assertRaises(ValueError,
                          randdecimal,
                          Decimal(10),
                          Decimal('5.33'))


def randdecimal(a, b):
    """
    Return a random decimal N such that a <= N <= b.
    """
    a, b = Decimal(a), Decimal(b)
    diff = b - a

    multiplier = pow(10, abs(diff.as_tuple()[2]))
    diff_to_int = int(diff * multiplier)

    return a + Decimal(randint(0, diff_to_int)) / multiplier


if __name__ == '__main__':
    unittest.main()