You're fairly certain, but with Python 3 you can be completely certain. That's the magic of it.

Python 2 will allow this to sometimes work, Python 3 will make sure this never works, because there's a bytes/text mismatch. It's nice to rule out entire classes of bugs like this

    from sys import argv
    import json
    with open(argv[1], 'rb') as f:
        json.loads(f.read())

Porting is still difficult. But when we ported from Py2 to Py3, we found a couple issues like this (despite dealing with weird encodings all the time).