def __add__(self, other):
if isinstance(other, BusinessPeriod):<EOL><INDENT>return self.add_period(other)<EOL><DEDENT>elif BusinessPeriod.is_businessperiod(other):<EOL><INDENT>return self + BusinessPeriod(other)<EOL><DEDENT>else:<EOL><INDENT>raise TypeError('<STR_LIT>' % type(other))<EOL><DEDENT>
addition of BusinessDate.

:param BusinessDate or BusinessPeriod or str other: can be BusinessPeriod or
any thing that might be casted to it.