pyRCV2/pyRCV2/numbers/rational_py.py

#   pyRCV2: Preferential vote counting
#   Copyright © 2020–2021  Lee Yingtong Li (RunasSudo)
#
#   This program is free software: you can redistribute it and/or modify
#   it under the terms of the GNU Affero General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU Affero General Public License for more details.
#
#   You should have received a copy of the GNU Affero General Public License
#   along with this program.  If not, see <https://www.gnu.org/licenses/>.

from pyRCV2.numbers.base import BasePyNum, compatible_types

from fractions import Fraction
import math

class Rational(BasePyNum):
	"""
	Wrapper for Python Fraction (rational arithmetic)
	"""
	
	_py_class = Fraction # For BasePyNum
	
	def pp(self, dp):
		"""Overrides BasePyNum.pp"""
		# TODO: Work out if there is a better way of doing this
		return format(float(self.impl), '.{}f'.format(dp))
	
	def round(self, dps, mode):
		"""Implements BaseNum.round"""
		factor = Fraction(10) ** dps
		if mode == Rational.ROUND_DOWN:
			return Rational._from_impl(math.floor(self.impl * factor) / factor)
		elif mode == Rational.ROUND_HALF_UP: # pragma: no cover
			raise NotImplementedError('ROUND_HALF_UP is not implemented in Python Rational context')
		elif mode == Rational.ROUND_HALF_EVEN:
			return Rational._from_impl(round(self.impl * factor) / factor)
		elif mode == Rational.ROUND_UP:
			return Rational._from_impl(math.ceil(self.impl * factor) / factor)
		else: # pragma: no cover
			raise ValueError('Invalid rounding mode')