title: I have no idea why this error: "missing 1 required positional argument: 'self'"
body: <p>This is my code:</p>
  
  <pre><code>
  from tkinter import Tk, Button
  import GUI
  
  root = Tk()
  b = GUI.time
  
  
  button1 = Button(
      root, text="Local time", command=b.local_time  # text on top of button
  )  # button click event handler
  button1.pack()
  
  button2 = Button(
      root, text="Greenwich time", command=b.greenwich_time  # text on top of button
  )  # button click event handler
  button2.pack()
  
  root.mainloop()
  </code></pre>
  
  <p>And gets the b.local_time and b.greenwich_time from my class time:</p>
  
  <pre><code>from time import strftime, localtime, gmtime
  class time:
      def __init__(self):
          self.gm_time = strftime("Day: %d %b %Y\nTime: %H:%M:%S %p\n", gmtime())
          self.l_time = strftime("Day: %d %b %Y\nTime: %H:%M:%S %p\n", localtime())
  
      def greenwich_time(self):
          print("Greenwich time:\n" + self.gm_time)
  
      def local_time(self):
          print("Local time:\n" + self.l_time)
  </code></pre>
  
  <p>But, when I click in the buttons, I get the errors:</p>
  
  <pre><code>Exception in Tkinter callback
  Traceback (most recent call last):
    File "C:\Users\carol\AppData\Local\Programs\Python\Python37-32\lib\tkinter\__init__.py", line 1705, in __call__
      return self.func(*args)
  TypeError: local_time() missing 1 required positional argument: 'self'
  
  Exception in Tkinter callback
  Traceback (most recent call last):
    File "C:\Users\carol\AppData\Local\Programs\Python\Python37-32\lib\tkinter\__init__.py", line 1705, in __call__
      return self.func(*args)
  TypeError: greenwich_time() missing 1 required positional argument: 'self'
  </code></pre>
  
  <p>Someone could explain to me why is missing the required argument??
  Thanks!!!</p>