underscore-single-leading-class.py

class Time:
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self._day = day

    def _is_even_number(self, x):
        return x % 2 == 0

time = Time(2020, 7, 10)
print(time.year, time.month, time._day)
# 2020 7 10
print(time._is_even_number(10))
# True