PIL problem, but only when called from within another object( Image doesn't exist) - image

Question

I am trying to develop a python app for a RaspberryPi on a PC. In order to test one aspect, I have written an object class to emulate an OLED display device (hardware) that the PC cannot use (no I2C). The Wdisp class is simply loaded in place of the hardware driver when using the PC.
I have another class that wraps up the few OLED functions I need ( write text , draw progressbar etc. )
# OLED display object
import os
Win = False
if os.name == 'nt':
Win=True
from WindowsOLED import Wdisp
else:
import Adafruit_GPIO.SPI as SPI
import Adafruit_SSD1306
from PIL import Image
from PIL import ImageDraw
from PIL import ImageFont
class OLEDDisplay(object):
def __init__(self):
# Raspberry Pi pin configuration:
RST = 24
if Win:
self.disp = Wdisp()
else:
self.disp = Adafruit_SSD1306.SSD1306_128_64(rst=RST)
# Initialize library.
self.disp.begin()
# Create blank image for drawing.
self.width = 128 #self.disp.width
self.height = 64 #self.disp.height
self._image = Image.new('1', (self.width, self.height))
self.draw = ImageDraw.Draw(self._image)
# Load default font.
self.font = ImageFont.load_default()
self.clear()
def __del__(self):
self.clear()
def __repr__(self):
return 'OLED display object for SSD1306 I2C'
def clear(self):
# Clear display
self.disp.clear()
self.disp.display()
def write(self, text):
self.draw.text((0, 2), text, font=self.font, fill=255)
self._show()
def progressbar(self, percent):
#draw a progress bar on top half of screen
shape_width = self.width * (percent/100)
padding =2
top = padding
bottom = (self.height/2) - padding
x = padding
self.draw.rectangle((x, top, self.width-padding, bottom), outline=255, fill=0)
self.draw.rectangle((x, top, x+shape_width, bottom), outline=255, fill=255)
self._show()
def loadimage(self, imagefile):
#open, convert and display an image
self._image = Image.open(imagefile).resize((self.disp.width,
self.disp.height),
Image.ANTIALIAS).convert('1')
self._show()
def _show(self):
# Display image.
self.disp.image(self._image)
self.disp.display()
If I test this class at the command line
Example:
>>> from OLEDDisplay import*
>>> OD = OLEDDisplay()
>>> OD.progressbar(50)
Its works fine - the OLEDDisplay object draws on a PIL image object, passes the image to the Wdisp object and the Wdisp object converts the image to a BitMapImage and displays in on a Tkinter Label ( self.L ).
#Windows subsitute OLED display class
#displays a label image for testing
from tkinter import *
from PIL import Image, ImageTk
from tkinter import filedialog, messagebox
from tkinter.constants import *
class Wdisp(object):
i=None
width = 128
height =64
_image = None
def __init__(self):
self.master = Tk()
self._image = Image.new('1', (self.width, self.height))
self.i = ImageTk.PhotoImage(self._image)
self.L= Label(self.master, text="label place holder", image=self.i)
self.L.pack(expand=YES, fill=BOTH)
def begin(self):
pass
def image(self, newimage):
self._image = newimage
def display(self):
#display the image
self.i = ImageTk.BitmapImage(self._image)
self.L.config(image=self.i)
However, if I use this in my app or test it in a small app:
from tkinter import *
from PIL import Image, ImageTk
from tkinter import filedialog, messagebox
from tkinter.constants import *
from OLEDDisplay import*
def updateOLED():
text = E.get
print(text)
OD.write(text)
master = Tk()
OD = OLEDDisplay()
E = Entry(master)
B = Button(master, text="update OLED", command = updateOLED)
E.pack()
B.pack()
It fails with a tkinter.TclError: image "pyimage4" doesn't exist:
Traceback (most recent call last):
File "D:\My Documents\PI Projects\Pyprojects\PTPIC\OLEDDisplay test.py", line 19, in <module>
OD = OLEDDisplay()
File "D:\My Documents\PI Projects\Pyprojects\PTPIC\OLEDDisplay.py", line 42, in __init__
self.clear()
File "D:\My Documents\PI Projects\Pyprojects\PTPIC\OLEDDisplay.py", line 52, in clear
self.disp.clear()
File "D:\My Documents\PI Projects\Pyprojects\PTPIC\WindowsOLED.py", line 45, in clear
self.display()
File "D:\My Documents\PI Projects\Pyprojects\PTPIC\WindowsOLED.py", line 36, in display
self.L.config(image=self.i)
File "C:\Python34\lib\tkinter\__init__.py", line 1324, in configure
return self._configure('configure', cnf, kw)
File "C:\Python34\lib\tkinter\__init__.py", line 1315, in _configure
self.tk.call(_flatten((self._w, cmd)) + self._options(cnf))
_tkinter.TclError: image "pyimage4" doesn't exist
I have no idea why : perhaps variable scope? perhaps something weird with PIL , so any suggestions welcome.
Cheers Bill