text: import pkgutil
  from .base import BaseCrawler
  import inspect
  
  
  # load classes subclass of BaseCrawler
  classes = []
  for loader, name, is_pkg in pkgutil.walk_packages(__path__):
      module = loader.find_module(name).load_module(name)
      for name, value in inspect.getmembers(module):
          globals()[name] = value
          if inspect.isclass(value) and issubclass(value, BaseCrawler) and value is not BaseCrawler \
                  and not getattr(value, 'ignore', False):
              classes.append(value)
  __all__ = __ALL__ = classes
  
  