def __init__(self, constants=None):
        """
        Default constructor for the L{Calendar} class.

        @type  constants: object
        @param constants: Instance of the class L{parsedatetime_consts.Constants}

        @rtype:  object
        @return: L{Calendar} instance
        """
          # if a constants reference is not included, use default
        if constants is None:
            self.ptc = Constants()
        else:
            self.ptc = constants

        self.weekdyFlag    = False  # monday/tuesday/...
        self.dateStdFlag   = False  # 07/21/06
        self.dateStrFlag   = False  # July 21st, 2006
        self.timeStdFlag   = False  # 5:50 
        self.meridianFlag  = False  # am/pm
        self.dayStrFlag    = False  # tomorrow/yesterday/today/..
        self.timeStrFlag   = False  # lunch/noon/breakfast/...
        self.modifierFlag  = False  # after/before/prev/next/..
        self.modifier2Flag = False  # after/before/prev/next/..
        self.unitsFlag     = False  # hrs/weeks/yrs/min/..
        self.qunitsFlag    = False  # h/m/t/d..

        self.timeFlag      = 0
        self.dateFlag      = 0