I saw the new setup.py in notebook shows:
    error = """
Notebook 6.0+ supports Python 3.5 and above.
When using Python 3.4 or earlier (including 2.7), please install Notebook 5.x.
Python {py} detected.
{pip}
""".format(py=sys.version_info, pip=pip_message )
So the new notebook just supports py>=3.5.
And I saw many codes like:
try: #PY3
    from base64 import encodebytes
except ImportError: #PY2
    from base64 import encodestring as encodebytes
Is it time to remove them?
I wanne try to do this.