added simple traffic light example

tk_first_steps/traffic_light_simple_mvc.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+
+from tkinter import *
+from tkinter import ttk
+
+# --------------------------
+# Model
+# --------------------------
+
+class TLight:
+    def __init__(self):
+        self.colors = {0: "red", 1: "yellow", 2: "green", 3: "yellow"}
+        self.status = 0
+        
+    def switch(self):
+        if self.status < max(self.colors.keys()):
+            self.status += 1
+        else:
+            self.status = 0
+            
+    def print_color(self):
+        print(self.colors[self.status])
+        
+    def get_color(self):
+        return self.colors[self.status]
+    
+# --------------------------
+# Controller
+# --------------------------
+
+class TLightController:
+    def __init__(self, app):
+        self.app = app
+        self.tlight = TLight()
+        
+    def change_light(self, event=None):
+        self.tlight.switch()
+        self.update_view()
+        
+    def update_view(self):
+        color = self.tlight.get_color()
+        self.app.change_light_display(color)
+        
+
+# --------------------------
+# View / Main Application
+# --------------------------
+
+class TLightApp(Tk):
+    def __init__(self):
+        super().__init__()
+        self.controller = TLightController(self)
+        
+        self.create_widgets()
+        self.create_light()
+        self.bind_events()
+        
+    def create_widgets(self):
+        mainframe = ttk.Frame(self, padding="3 3 3 3")
+        mainframe.grid(column=0, row=0, sticky=N+W+S+E)
+        self.columnconfigure(0, weight=1)
+        self.rowconfigure(0, weight=1)
+        
+        button_switch = ttk.Button(mainframe, text="Schalte um", command=self.controller.change_light)
+        button_switch.grid(column=0, row=0, sticky=W)
+                light_canvas = Canvas(mainframe, width=50, height=50, background="black")
+        light_canvas.grid(column=1, row=0, sticky=W)
+        self.lc = light_canvas
+        
+    def create_light(self, color="red"):
+        self.light = self.lc.create_oval(10,10,40,40,fill=color)
+        
+    def bind_events(self):
+        self.bind("<Return>", self.controller.change_light)
+    
+    def change_light_display(self, color):
+        self.lc.itemconfigure(self.light, fill=color)
+        
+# --------------------------
+# Execution
+# --------------------------
+if __name__ == "__main__":
+    app = TLightApp()
+    app.mainloop()