title: AttributeError: 'str' object has no attribute 'keys'
body: <p>The following is a simple tkinter program that displays an empty window:</p>
  
  <pre><code># firstTkinter2.py
  from Tkinter import Tk, Label
  top = Tk()
  l = Label(top, "Hello World")
  l.pack()
  # Give the window a title.
  top.title("My App")
  # Change the minimum size.
  top.minsize(400, 400)
  # Change the background colour.
  top.configure(bg = "green")
  # Run the widget.
  top.mainloop()
  </code></pre>
  
  <p>I run the above code but it encountered an error:</p>
  
  <pre><code>zhiwei@zhiwei-Lenovo-Rescuer-15ISK:~/Documents/python programs/tkinter$ python tk2.py
  Traceback (most recent call last):
    File "tk2.py", line 4, in &lt;module&gt;
      l = Label(top, "Hello World")
    File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2600, in __init__
      Widget.__init__(self, master, 'label', cnf, kw)
    File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2094, in __init__
      for k in cnf.keys():
  AttributeError: 'str' object has no attribute 'keys'
  </code></pre>
  
  <p>How can I fix this error and let it run properly?</p>