title: How to fix "- _tkinter.TclError: no events specified in binding"
body: <p>I found the source code somewhere on the internet
  a simple program to create a window with the option
  entering mathematical operations and displaying from the keyboard
  the result.This is code:</p>
  
  <pre><code>import tkinter as tk
  from math import *
  
  def evaluate(event):
      res.configure(text="Result: " + str(eval(entry.get())))
  
  w = tk.Tk()
  tk.Label(w, text="Your Expression:").pack()
  entry = tk.Entry(w)
  entry.bind("event", evaluate)
  entry.pack()
  res = tk.Label(w)
  res.pack()
  w.mainloop()
  </code></pre>
  
  <p>I'm getting an error:</p>
  
  <blockquote>
    <p>C:\Users\rob\PycharmProjects\untitled2\venv\Scripts\python.exe
    "C:/Users/rob/Desktop/new test.py" Traceback (most recent call last): 
    File "C:/Users/rob/Desktop/new test.py", line 12, in 
        entry.bind("", evaluate)   File "C:\Users\rob\AppData\Local\Programs\Python\Python37\lib\tkinter__init__.py",
    line 1248, in bind
        return self._bind(('bind', self._w), sequence, func, add)   File "C:\Users\rob\AppData\Local\Programs\Python\Python37\lib\tkinter__init__.py",
    line 1203, in _bind
        self.tk.call(what + (sequence, cmd))
    _tkinter.TclError: no events specified in binding</p>
  </blockquote>
  
  <p>Please help. Im starting learning Python and I don't know a solution.</p>