def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def _split_vertical(container):
		r1 = None
		r2 = None
		min_w = int(W_RATIO*container.h)+1
		if container.w < 2*min_w:
			return None
		r1 = Container(container.x,container.y,randint(min_w, container.w-min_w),container.h)
		r2 = Container(container.x+r1.w,container.y,container.w-r1.w,container.h)
		return [r1, r2]