python中的嵌套类（内部类调用外部类中的方法函数）

class DiagramFactory:

    @classmethod
    def make_diagram(Class, width, height):
        return Class.Diagram(width, height)


    @classmethod
    def make_rectangle(Class, x, y, width, height, fill="white",
            stroke="black"):
        return Class.Rectangle(x, y, width, height, fill, stroke)

    @classmethod
    def make_text(Class, x, y, text, fontsize=12):
        return Class.Text(x, y, text, fontsize)


    BLANK = " "
    CORNER = "+"
    HORIZONTAL = "-"
    VERTICAL = "|"


    class Diagram:

        def __init__(self, width, height):
            self.superclass = DiagramFactory()
            self.width = width
            self.height = height
            self.diagram = DiagramFactory._create_rectangle(self.superclass,self.width, self.height, DiagramFactory.BLANK)


        def add(self, component):
            for y, row in enumerate(component.rows):
                for x, char in enumerate(row):
                    self.diagram[y + component.y][x + component.x] = char


        def save(self, filenameOrFile):
            file = (None if isinstance(filenameOrFile, str) else
                    filenameOrFile)
            try:
                if file is None:
                    file = open(filenameOrFile, "w")
                for row in self.diagram:
                    print >>file, "".join(row)
            finally:
                if isinstance(filenameOrFile, str) and file is not None:
                    file.close()


    class Rectangle:

        def __init__(self, x, y, width, height, fill, stroke):
            self.superclass = DiagramFactory()
            self.x = x
            self.y = y
            self.rows = DiagramFactory._create_rectangle(self.superclass, width, height,
                    DiagramFactory.BLANK if fill == "white" else "%")


    class Text:

        def __init__(self, x, y, text, fontsize):
            self.x = x
            self.y = y
            self.rows = [list(text)]


    def  _create_rectangle(self, width, height, fill):
        rows = [[fill for _ in range(width)] for _ in range(height)]
        for x in range(1, width - 1):
            rows[0][x] = DiagramFactory.HORIZONTAL
            rows[height - 1][x] = DiagramFactory.HORIZONTAL
        for y in range(1, height - 1):
            rows[y][0] = DiagramFactory.VERTICAL
            rows[y][width - 1] = DiagramFactory.VERTICAL
        for y, x in ((0, 0), (0, width - 1), (height - 1, 0),
                (height - 1, width -1)):
            rows[y][x] = DiagramFactory.CORNER
        return rows