'Plus corresponds to unary prefix plus in Python.
The operation is evaluated using the same rules as add; the
operation plus(a) is calculated as add(\'0\', a) where the \'0\'
has the same exponent as the operand.
>>> ExtendedContext.plus(Decimal(\'1.3\'))
Decimal(\'1.3\')
>>> ExtendedContext.plus(Decimal(\'-1.3\'))
Decimal(\'-1.3\')
>>> ExtendedContext.plus(-1)
Decimal(\'-1\')'

def plus(self, a):

    a = _convert_other(a, raiseit=True)
    return a.__pos__(context=self)
