def __init__(self, tax_brackets_configuration):
self.tax_brackets = []
for bracket in tax_brackets_configuration['brackets']:
new_bracket = TaxBracket(bracket['income'], bracket['rate'])
self.tax_brackets.append(new_bracket)
self.top_marginal_bracket = TaxBracket(
Decimal('Infinity'),
tax_brackets_configuration['top_marginal_rate'])
logging.info(
f"Initialized with {len(tax_brackets_configuration['brackets'])} " \
f"brackets, top marginal rate of "\
f"{tax_brackets_configuration['top_marginal_rate']}"
)
class TaxBracketCollection:
def __init__(self, tax_brackets_configuration):
self.tax_brackets = []
for bracket in tax_brackets_configuration['brackets']:
new_bracket = TaxBracket(bracket['income'], bracket['rate'])
self.tax_brackets.append(new_bracket)
self.top_marginal_bracket = TaxBracket(
Decimal('Infinity'),
tax_brackets_configuration['top_marginal_rate'])
logging.info(
f"Initialized with {len(tax_brackets_configuration['brackets'])} " \
f"brackets, top marginal rate of "\
f"{tax_brackets_configuration['top_marginal_rate']}"
)
def calculate_tax(self, income):
if income < 0:
raise Exception("Negative incomes are not supported")
total_tax = 0
for bracket in self.tax_brackets:
if income == 0:
break
taxable_in_bracket = min(income, bracket.income)
total_tax += bracket.calculate_tax(taxable_in_bracket)
income -= taxable_in_bracket
if income > 0:
total_tax += self.top_marginal_bracket.calculate_tax(income)
return total_tax
def effective_tax_rate(self, income):
# We could improve performance here by saving / memoizing the value
# of "calculate_tax" if we called it earlier, at the expense of making
# TaxBracketCollection stateful.
total_tax = self.calculate_tax(income)
return format(total_tax / income, '.2f')
def test_calculate_tax_below_limit(self):
bracket = TaxBracket(100000, 0.10)
self.assertEqual(bracket.calculate_tax(3000), 300)
def test_init(self):
bracket = TaxBracket(100000, 0.10)
self.assertTrue(isinstance(bracket, TaxBracket))
def test_error_negative_rate(self):
with self.assertRaises(Exception):
bracket = TaxBracket(1, -0.10)
def test_error_negative_income(self):
with self.assertRaises(Exception):
bracket = TaxBracket(-1, 0.10)
def test_error_calculate_tax_beyond_limit(self):
bracket = TaxBracket(100000, 0.10)
with self.assertRaises(Exception):
bracket.calculate_tax(200000)
def test_does_not_round_to_two_decimal_places(self):
# Intentional decision not to round to two decimal places (ie. cents)
# until the end. More description in utils.py.
bracket = TaxBracket(100000, 0.19)
self.assertEqual(bracket.calculate_tax(7.10), 1.349)