input: Write a function to explain the difference between a list and a tuple in Python. If the input is 'list', return 'Mutable, changeable data structure with square brackets'. If the input is 'tuple', return 'Immutable, fixed data structure with parentheses'. For any other input, return 'Invalid input'.
  assert explain_data_types('list')=='Mutable, changeable data structure with square brackets'
  assert explain_data_types('tuple')=='Immutable, fixed data structure with parentheses'
  assert explain_data_types('dictionary')=='Invalid input'
  assert explain_data_types('set')=='Invalid input'
  assert explain_data_types('')=='Invalid input'
output: def explain_data_types(input_type):
      if input_type == 'list':
          return 'Mutable, changeable data structure with square brackets'
      elif input_type == 'tuple':
          return 'Immutable, fixed data structure with parentheses'
      else:
          return 'Invalid input'