Validate date parameters sent in a request object using either custom start/end dates or predefined periods. Raise exception if invalid. Python 3.

Requester.py

import datetime
import re


class Requester:
    start = None
    end = None
    now = datetime.date.today()

    default_period = {
        "this_week": (0, 7),
        "last_week": (7, 14),
        "this_month": (0, 30),
        "last_month": (30, 60),
        "this_year": (0, 365),
        "last_year": (365, 730),
        "last_ninety": (0, 90)
    }

    def __init__(self, request):
        self.start_date = request.args.get('start_date')
        self.end_date = request.args.get('end_date')
        self.period = request.args.get('period')
        self.sort = request.args.get('sort')

        if self.period:
            self.start, self.end = self._get_period_dates(self.period)

        if self.start_date:
            self._validate_custom_dates(self.start_date, self.end_date)
            self.start = self._str_to_date(self.start_date)
            self.end = self._str_to_date(self.end_date) if self.end_date else self.now

    def _get_period_dates(self, period):
        """
        Set start/end date based on default time period
        :param period:
        """
        period = period.lower()
        if period in self.default_period.keys():
            end, start = self.default_period[period]
            start_date = self.now - datetime.timedelta(days=start)
            end_date = self.now if not end else self.now - datetime.timedelta(days=end)

            return start_date, end_date

        # raise error and return valid options
        options = ', '.join(['{}' for _ in range(len(self.default_period))])
        options = options.format(*self.default_period.keys())
        raise ValueError("Period parameter is invalid. Options: {}".format(options))

    @staticmethod
    def _validate_custom_dates(start, end):
        """
        Validate that the start/end date string formats are correct
        :param start:
        :param end:
        """
        for date in [start, end]:
            if not isinstance(date, str):
                continue

            valid_date = re.search("(.{4}-.{2}-.{2})+$", date)
            if not valid_date:
                raise ValueError("Start or end date parameter is invalid. Valid format: YYYY-MM-DD")

    @staticmethod
    def _str_to_date(date):
        """
        Convert date string to datetime.date() object.
        Format: 'YYYY-MM-DD'
        :param date:
        """
        try:
            date_obj = datetime.datetime.strptime(date, '%Y-%m-%d').date()
        except ValueError:
            raise ValueError("Invalid date. Please check the start/end parameters.")

        return date_obj