The error log is

...\fire\core.py", line 775, in _ParseArgs
    accepts_positional_args = metadata.get(decorators.ACCEPTS_POSITIONAL_ARGS)
AttributeError: 'NoneType' object has no attribute 'get'

From https://github.com/google/python-fire/blob/master/fire/decorators.py#L87

def GetMetadata(fn):
  # Class __init__ functions and object __call__ functions require flag style
  # arguments. Other methods and functions may accept positional args.
  default = {
      ACCEPTS_POSITIONAL_ARGS: inspect.isroutine(fn),
  }
  return getattr(fn, FIRE_METADATA, default)

GetMetadata uses getattr to retrieve the fire metadata from component fn. In this case, fn is a bs4.BeautifulSoup.

For bs4.BeautifulSoup (bs4/__init__.py#L68), it inherits from class bs4.Tag, which overrides __getattr__ (bs4/element.py#L1433).

def __getattr__(self, tag):
        """Calling tag.subtag is the same as calling tag.find(name="subtag")"""
        ...

So getattr(fn, FIRE_METADATA, default) for a BeautifulSoup instance always return None for the non-existing subtag, and calling metadata.get later raises the above exception.

A quick fix is to check if the getattr result is a dict with key ACCEPTS_POSITIONAL_ARGS, and return default if it is not.

Thanks for diving into that @WaizungTaam! Your suggested fix sounds good to me.