Some examples in the documentation don't work with Python 3

[rutsky]

For example this one:

>>> from docker import Client
>>> cli = Client(base_url='tcp://127.0.0.1:2375')
>>> for line in cli.pull('busybox', stream=True):
...     print(json.dumps(json.loads(line), indent=4))

will produce:

TypeError: the JSON object must be str, not 'bytes'

Maybe explicitly document such differences, e.g. by adding something like "Note: On Python 3 you need to decode line from bytes to str: json.loads(line.decode())"?

[dnephin]

I noticed this while adding python3 support to compose. The streams that you receive from stream=True calls are bytes (I was expecting str).

There is an option to have the endpoint return already loaded (which handles the encoding). It would be nice to get streams of str, but that would be a breaking change, so I'm not sure we can do it initially.

We can at least update the examples to include the encode.

[grahamlyons]

Python 3 users will already be used to dealing with byte-decoding so documenting this would be the best approach.

Altering the return types of these methods to indicate either str or bytes would be relatively simple:
https://github.com/docker/docker-py/blob/6fe1c7f/docker/models/containers.py#L228-L229

How about changing those mentions to something like this:

        Returns:
            (generator or str|bytes): Logs from the container.