Unknown GridFS.read says:
The bytes are returned as an instance of :class:`str` (:class:`bytes` in python 3).
We don't support python 2 anymore so these docs should only describe the Python 3 behavior.
This problem is widespread across the docs:
$ git grep 'in python 3' bson/__init__.py:669: # Keys can only be text in python 3. bson/__init__.py:1004: :class:`basestring` (:class:`str` in python 3). Raises bson/__init__.py:1301: :class:`str` (:class:`bytes` in python 3). Returns ``True`` bson/__init__.py:1338: :class:`basestring` (:class:`str` in python 3). Raises bson/_cbsonmodule.c:3010: /* PyCapsule is new in python 3.1 */ bson/code.py:26: :class:`basestring` (:class:`str` in python 3) or `scope` bson/dbref.py:44: an instance of :class:`basestring` (:class:`str` in python 3). bson/objectid.py:188: in python 3), ObjectId) and InvalidId if it is not a doc/changelog.rst:2018:trivial wrapper around long (in python 2.x) or int (in python 3.x). This gridfs/grid_file.py:596: in python 3). If `size` is negative or omitted all data is read. pymongo/collection.py:124: :class:`basestring` (:class:`str` in python 3). Raises pymongo/collection.py:1946: (:class:`str` in python 3), and the direction(s) must be one of pymongo/collection.py:2639: (:class:`str` in python 3). Raises :class:`~pymongo.errors.InvalidName` pymongo/collection.py:2703: :class:`basestring` (:class:`str` in python 3). pymongo/cursor.py:882: :class:`basestring` (:class:`str` in python 3). pymongo/cursor.py:980: (:class:`str` in python 3) or :class:`~bson.code.Code` pymongo/cursor.py:992: :class:`basestring` (:class:`str` in python 3). Raises pymongo/database.py:83: :class:`basestring` (:class:`str` in python 3). Raises pymongo/database.py:718: (:class:`str` in python 3) then the command {`command`: `value`} pymongo/mongo_client.py:1879: :class:`basestring` (:class:`str` in python 3) or pymongo/operations.py:439: (:class:`str` in python 3), and the direction(s) must be one of test/test_bson.py:533: # as keys in python 3.x. Using binary data as a key makes