def __init__(self, bson_bytes, codec_options=None):
        """Create a new :class:`RawBSONDocument`

        :class:`RawBSONDocument` is a representation of a BSON document that
        provides access to the underlying raw BSON bytes. Only when a field is
        accessed or modified within the document does RawBSONDocument decode
        its bytes.

        :class:`RawBSONDocument` implements the ``Mapping`` abstract base
        class from the standard library so it can be used like a read-only
        ``dict``::

            >>> raw_doc = RawBSONDocument(BSON.encode({'_id': 'my_doc'}))
            >>> raw_doc.raw
            b'...'
            >>> raw_doc['_id']
            'my_doc'

        :Parameters:
          - `bson_bytes`: the BSON bytes that compose this document
          - `codec_options` (optional): An instance of
            :class:`~bson.codec_options.CodecOptions` whose ``document_class``
            must be :class:`RawBSONDocument`. The default is
            :attr:`DEFAULT_RAW_BSON_OPTIONS`.

        .. versionchanged:: 3.8
          :class:`RawBSONDocument` now validates that the ``bson_bytes``
          passed in represent a single bson document.

        .. versionchanged:: 3.5
          If a :class:`~bson.codec_options.CodecOptions` is passed in, its
          `document_class` must be :class:`RawBSONDocument`.
        """
        self.__raw = bson_bytes
        self.__inflated_doc = None
        # Can't default codec_options to DEFAULT_RAW_BSON_OPTIONS in signature,
        # it refers to this class RawBSONDocument.
        if codec_options is None:
            codec_options = DEFAULT_RAW_BSON_OPTIONS
        elif codec_options.document_class is not RawBSONDocument:
            raise TypeError(
                "RawBSONDocument cannot use CodecOptions with document "
                "class %s" % (codec_options.document_class, ))
        self.__codec_options = codec_options
        # Validate the bson object size.
        _get_object_size(bson_bytes, 0, len(bson_bytes))
Create a new :class:`RawBSONDocument`

        :class:`RawBSONDocument` is a representation of a BSON document that
        provides access to the underlying raw BSON bytes. Only when a field is
        accessed or modified within the document does RawBSONDocument decode
        its bytes.

        :class:`RawBSONDocument` implements the ``Mapping`` abstract base
        class from the standard library so it can be used like a read-only
        ``dict``::

            >>> raw_doc = RawBSONDocument(BSON.encode({'_id': 'my_doc'}))
            >>> raw_doc.raw
            b'...'
            >>> raw_doc['_id']
            'my_doc'

        :Parameters:
          - `bson_bytes`: the BSON bytes that compose this document
          - `codec_options` (optional): An instance of
            :class:`~bson.codec_options.CodecOptions` whose ``document_class``
            must be :class:`RawBSONDocument`. The default is
            :attr:`DEFAULT_RAW_BSON_OPTIONS`.

        .. versionchanged:: 3.8
          :class:`RawBSONDocument` now validates that the ``bson_bytes``
          passed in represent a single bson document.

        .. versionchanged:: 3.5
          If a :class:`~bson.codec_options.CodecOptions` is passed in, its
          `document_class` must be :class:`RawBSONDocument`.
        
stackoverflow/venv/lib/python3.6/site-packages/bson/raw_bson.py