input: Write a function that generates a Python class for an online store item that includes fields for ID, name, price, and description. If the input is valid, return the class definition. If the input is invalid, return an error message.
  
  assert generate_store_item_class() == '''
  class StoreItem:
      def __init__(self, item_id, name, price, description):
          self.item_id = item_id
          self.name = name
          self.price = price
          self.description = description
  
      def __str__(self):
          return f'{self.name}, ${self.price}'
  
      def to_dict(self):
          return {
              'item_id': self.item_id,
              'name': self.name,
              'price': self.price,
              'description': self.description
          }
  '''
  assert generate_store_item_class('invalid input') == 'Invalid input: expected no arguments, received 1'
output: def generate_store_item_class(*args):
      if len(args) != 0:
          return 'Invalid input: expected no arguments, received ' + str(len(args))
      return '''
  class StoreItem:
      def __init__(self, item_id, name, price, description):
          self.item_id = item_id
          self.name = name
          self.price = price
          self.description = description
  
      def __str__(self):
          return f'{self.name}, ${self.price}'
  
      def to_dict(self):
          return {
              'item_id': self.item_id,
              'name': self.name,
              'price': self.price,
              'description': self.description
          }
  '''