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):
        self.g = g
        r = 5
        # 繪出三個頂點
        self.p1.drawMe(self.g,r)
        self.p2.drawMe(self.g,r)
        self.p3.drawMe(self.g,r)
        line1 = Line(self.p1,self.p2)
        line2 = Line(self.p1,self.p3)
        line3 = Line(self.p2,self.p3)
        # 繪出三邊線
        line1.drawMe(self.g)
        line2.drawMe(self.g)
        line3.drawMe(self.g)