fix: invalidate the previous contents before populating with new weather

weather.py

@@ -93,6 +93,7 @@ def __init__(self, master, city):
                                     font=("Helvetica", 10, "bold"))
             label_empty_str.place(relx=0.5, rely=0.5, anchor="center")
             label_empty_str.pack(fill=BOTH, expand=1, padx=4, pady=4)
+
         button_city.config(state=NORMAL)
 
     # get the weather information of the passed city id
@@ -254,8 +255,8 @@ def button_state_check(self):
 def show():
     city = entry_city.get()
     print city
-    content_frame = Frame(root)
-    content_frame.grid(row=1, columnspan=2)
+    for child in content_frame.winfo_children():
+        child.destroy()
     Weather(content_frame, city)
 
 root = Tk()
@@ -280,6 +281,9 @@ def show():
 entry_city.grid(row=0, column=1, padx=4, pady=4)
 entry_city.focus_set()
 
+content_frame = Frame(root)
+content_frame.grid(row=1, columnspan=2)
+
 button_city = Button(top_frame, text="Show Weather", command=show, font=font, relief=GROOVE)
 button_city.grid(row=1, columnspan=2, padx=4, pady=4)