Python calculates the circumference the area the volume of the sphere and draws the circle

Input radius, calculate the circumference of the circle, the area, the volume of the sphere, and draw the circle.
Drag bar, input box and image control data to stay the same!

Test passed under Fedora

#https://github.com/RobberPhex/GTK-Example-CalcArea
from gi.repository import Gtk, Gdk, GdkPixbuf
from PIL import Image, ImageDraw
from io import BytesIO
from math import pi
class Model:
    '''
     Model class 
     Storage radius, calculate circumference, area, volume 
    '''
    def __init__(self):
        self._radius = 0
    def setRadius(self, radius):
        self._radius = float(radius)
    def getRadius(self):
        return self._radius
    def getPerimeter(self):
        return pi * self._radius * 2
    def getArea(self):
        return self._radius ** 2 * pi
    def getVolume(self):
        return 4 * pi * self._radius ** 3 / 3

class Controller:
    '''
     The controller class 
     Controls the updating of views and models 
    '''
    def __init__(self, model):
        self.model = model
        self._observers = []
    def addObserver(self, observer):
        self._observers.append(observer)
    def setRadius(self, radius):
        model.setRadius(radius)
        self.notify()
    def notify(self):
        for observer in self._observers:
            observer.update()

class TextView:
    '''
     Text view class 
     View that handles text input fields 
    '''
    def __init__(self, model, rEntry, pEntry, aEntry, vEntry):
        '''
        :type model Model
        '''
        self.model = model
        self.rEntry = rEntry
        self.pEntry = pEntry
        self.aEntry = aEntry
        self.vEntry = vEntry
    def update(self):
        self.rEntry.set_text('%2.2f' % self.model.getRadius())
        self.pEntry.set_text('%2.2f' % self.model.getPerimeter())
        self.aEntry.set_text('%2.2f' % self.model.getArea())
        self.vEntry.set_text('%2.2f' % self.model.getVolume())

class ScaleView:
    '''
     Drag bar view 
     View that handles drag bars 
    '''
    def __init__(self, model, scale):
        '''
        :type model Model
        '''
        self.model = model
        self.scale = scale
    def update(self):
        self.scale.set_value(self.model.getRadius())

class ImageView:
    '''
     Image view 
     View of the image 
    '''
    @classmethod
    def imgToPixbuf(cls, img):
        '''
        :type img Image
        '''
        buff = BytesIO()
        img.save(buff, 'ppm')
        contents = buff.getvalue()
        buff.close()
        loader = GdkPixbuf.PixbufLoader.new_with_type('pnm')
        loader.write(contents)
        pixbuf = loader.get_pixbuf()
        loader.close()
        return pixbuf
    @classmethod
    def ellipse(cls, radius):
        '''
        :type radius int
        '''
        image = Image.new("RGBA", (300, 300), "white")
        draw = ImageDraw.Draw(image)
        minor = 150 - radius
        major = 150 + radius
        draw.ellipse((minor, minor, major, major), outline='red')
        pixbuf = ImageView.imgToPixbuf(image)
        return pixbuf
    def __init__(self, model, image):
        self.model = model
        self.image = image
    def update(self):
        radius = self.model.getRadius()
        pixbuf = ImageView.ellipse(radius)
        self.image.set_from_pixbuf(pixbuf)

class MainWindow(Gtk.Window):
    '''
     The main window class 
     Responsible for the display of the overall interface 
    '''
    def textCallback(self, widget, controller):
        '''
         Text input callback 
        '''
        try:
            radius = float(widget.get_text())
            controller.setRadius(radius)
        except ValueError as e:
            pass
    def scaleCallback(self, widget, controller):
        '''
         Drag a bar callback 
        '''
        radius = widget.get_value()
        controller.setRadius(radius)
    def __init__(self):
        Gtk.Window.__init__(self, title="Title")
        self.set_default_size(600, 400)
        self.set_position(Gtk.WindowPosition.CENTER)
        hbox = Gtk.HBox(spacing=5)
        self.add(hbox)
        vbox = Gtk.VBox(spacing=5)
        hbox.pack_start(vbox, True, True, 2)
        table = Gtk.Table.new(4, 2, False)
        vbox.pack_start(table, True, True, 2)
        label = Gtk.Label(' Radius: ')
        table.attach_defaults(label, 0, 1, 0, 1)
        label = Gtk.Label(' Circumference: ')
        table.attach_defaults(label, 0, 1, 1, 2)
        label = Gtk.Label(' Area: ')
        table.attach_defaults(label, 0, 1, 2, 3)
        label = Gtk.Label(' Volume: ')
        table.attach_defaults(label, 0, 1, 3, 4)
        self.radiusEntry = Gtk.Entry.new()
        self.radiusEntry.connect('changed', self.textCallback, controller)
        table.attach_defaults(self.radiusEntry, 1, 2, 0, 1)
        self.perimeterEntry = Gtk.Entry.new()
        self.perimeterEntry.set_sensitive(False)
        self.perimeterEntry.set_text(' The perimeter ')
        table.attach_defaults(self.perimeterEntry, 1, 2, 1, 2)
        self.areaEntry = Gtk.Entry.new()
        self.areaEntry.set_sensitive(False)
        self.areaEntry.set_text(' area ')
        table.attach_defaults(self.areaEntry, 1, 2, 2, 3)
        self.volumeEntry = Gtk.Entry.new()
        self.volumeEntry.set_sensitive(False)
        self.volumeEntry.set_text(' volume ')
        table.attach_defaults(self.volumeEntry, 1, 2, 3, 4)
        self.scale = Gtk.HScale.new_with_range(0, 100, 1)
        self.scale.connect('value-changed', self.scaleCallback, controller)
        vbox.pack_start(self.scale, False, False, 2)
        pixbuf = GdkPixbuf.Pixbuf.new(GdkPixbuf.Colorspace.RGB, True, 8, 300, 300)
        pixbuf.fill(0xaaaaaaaa)
        self.image = Gtk.Image.new_from_pixbuf(pixbuf)
        hbox.pack_start(self.image, True, True, 2)
        self.connect('delete-event', Gtk.main_quit)

model = Model()
controller = Controller(model)
if __name__ == '__main__':
    Gdk.threads_init()
    Gdk.threads_enter()
    win = MainWindow()
    iv = ImageView(model, win.image)
    controller.addObserver(iv)
    tv = TextView(model, win.radiusEntry, win.perimeterEntry, win.areaEntry, win.volumeEntry)
    controller.addObserver(tv)
    sv = ScaleView(model, win.scale)
    controller.addObserver(sv)
    win.show_all()
    Gtk.main()
    Gdk.threads_leave()

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