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 drawMe(self, g, r):
        self.g = g
        self.r = r
        self.g.save()
        self.g.moveTo(self.x,self.y)
        self.g.beginPath()
        # 根據 r 半徑繪製一個圓代表點的所在位置
        self.g.arc(self.x, self.y, self.r, 0, 2*math.pi, true)
        self.g.moveTo(self.x,self.y)
        self.g.lineTo(self.x+self.r, self.y)
        self.g.moveTo(self.x, self.y)
        self.g.lineTo(self.x-self.r, self.y)
        self.g.moveTo(self.x, self.y)
        self.g.lineTo(self.x, self.y+self.r)
        self.g.moveTo(self.x, self.y)
        self.g.lineTo(self.x, self.y-self.r)
        self.g.restore()
        self.g.stroke()