def remove(self, elem):
        """Remove a requirement.

        :param elem: a string or :class:`Requirement` instance.
        """
        if isinstance(elem, text_type):
            for requirement in self:
                if requirement.package == elem:
                    return super(Requirements, self).remove(requirement)
        return super(Requirements, self).remove(elem)
def getT(self):
        x = self.p2.x - self.p1.x
        y = self.p2.y - self.p1.y
        if (math.fabs(x) < math.pow(10,-100)):
            if(y < 0.0):
                return (-math.pi/2)
            else:
                return (math.pi/2)
        else:
            return math.atan2(y, x)