>>> import difflib
>>> a = ["spam", "eggs", "spammy", "eggy"]
>>> b = 'spam'
>>> sorted(a, key=lambda x: difflib.SequenceMatcher(None, x, b).ratio())
['eggy', 'eggs', 'spammy', 'spam']
Also, if you want the reverse order:
>>> sorted(a, key=lambda x: difflib.SequenceMatcher(None, x, b).ratio(), reverse=True)
['spam', 'spammy', 'eggs', 'eggy']