假设我了解你想要什么,
>>> collections.Counter([x for sublist in a for x in sublist])
Counter({'mrpycharm': 3, 'its': 2, 'friends': 1, 'is': 1, 'it': 1, 'hello': 1})
要么,
>>> c = collections.Counter()
>>> for sublist in a:
... c.update(sublist)
...
>>> c
Counter({'mrpycharm': 3, 'its': 2, 'friends': 1, 'is': 1, 'it': 1, 'hello': 1})