docs: def exists(self, document_or_id=None, **kwargs):
          """Check if a file exists in this instance of :class:`GridFS`.
  
          The file to check for can be specified by the value of its
          ``_id`` key, or by passing in a query document. A query
          document can be passed in as dictionary, or by using keyword
          arguments. Thus, the following three calls are equivalent:
  
          >>> fs.exists(file_id)
          >>> fs.exists({"_id": file_id})
          >>> fs.exists(_id=file_id)
  
          As are the following two calls:
  
          >>> fs.exists({"filename": "mike.txt"})
          >>> fs.exists(filename="mike.txt")
  
          And the following two:
  
          >>> fs.exists({"foo": {"$gt": 12}})
          >>> fs.exists(foo={"$gt": 12})
  
          Returns ``True`` if a matching file exists, ``False``
          otherwise. Calls to :meth:`exists` will not automatically
          create appropriate indexes; application developers should be
          sure to create indexes if needed and as appropriate.
  
          :Parameters:
            - `document_or_id` (optional): query document, or _id of the
              document to check for
            - `**kwargs` (optional): keyword arguments are used as a
              query document, if they're present.
          """
          if kwargs:
              return self.__files.find_one(kwargs, ["_id"]) is not None
          return self.__files.find_one(document_or_id, ["_id"]) is not None