my z-table in python

z_table.py

from math import sqrt, erf, erfc

from scipy.special import erfinv, erfcinv


class Table:
    def __init__(self, precision=4):
        self.precision = precision

    def below(self, z_score):
        return round(0.5 + 0.5 * erf(z_score / sqrt(2)), self.precision)

    def above(self, z_score):
        return round(0.5 * erfc(z_score / sqrt(2)), self.precision)

    def lower_percentage(self, percentage):
        return round(sqrt(2) * erfinv((percentage - 0.5) / 0.5), self.precision)

    def upper_percentage(self, percentage):
        return round(sqrt(2) * erfcinv(percentage / 0.5), self.precision)

    def __repr__(self):
        return 'Math.Table({})'.format(self.precision)

if __name__ == '__main__':
    z = Table()
    print(z.below(0.5))
    print(z.above(0.5))
    print(z.lower_percentage(0.25))
    print(z.upper_percentage(0.25))