im_a_banana.py

from Tkinter import *
from PIL     import Image, ImageTk

class Banana(object):
  def __init__(self, root):
    self.img = self.dimg = Image.open("im_a_banana.jpg")
    self.dimensions = self.dd = self.img.size
    self.root = root
    self.l = Label(self.root)
    self.redraw_image()

  def redraw_image(self):
    self.the_proper_banana = ImageTk.PhotoImage(self.img)
    self.l.configure(image=self.the_proper_banana)

  def resize(self, width, height):
    self.img = self.dimg.resize((width, height), Image.ANTIALIAS)
    self.redraw_image()

  def resize_with_dimensions(self):
    self.resize(self.dimensions[0], self.dimensions[1])

  def zoom_in(self):
    self.dimensions = map(lambda x: int(x * 1.1), self.dimensions)
    self.resize_with_dimensions()

  def zoom_out(self):
    self.dimensions = map(lambda x: int(x * 0.9), self.dimensions)
    self.resize_with_dimensions()

  def regular_zoom(self):
    self.dimensions = self.dd
    self.img = self.dimg
    self.resize_with_dimensions()


root = Tk()
root.title("I'm a banana!")
root.minsize(400, 300)
root.aspect(4, 3, 4, 3)
f = Frame(root, padx=50, pady=50, width=400, height=300)
f.pack()

banana = Banana(f)
in_b  = Button(f, text="Zoom In",      command=banana.zoom_in)
out_b = Button(f, text="Zoom Out",     command=banana.zoom_out)
reg_b = Button(f, text="Regular Zoom", command=banana.regular_zoom)

banana.l.grid(row=0, columnspan=3, column=1)
in_b.grid(row=1,  column=1)
reg_b.grid(row=1, column=2)
out_b.grid(row=1, column=3)

root.bind("=", lambda e: banana.zoom_in())
root.bind("-", lambda e: banana.zoom_out())
root.bind("<space>", lambda e: banana.regular_zoom())
root.bind("q", lambda e: e.widget.quit())
root.mainloop()