input: Write a function to validate input as integer in a tkinter Entry widget.
  assert validate_input('123') == True
  assert validate_input('abc') == False
  assert validate_input('') == True
output: def validate_input(input_value):
      if input_value == '':
          return True
      try:
          int(input_value)
          return True
      except ValueError:
          return False