>>> lst = ['diamons_6', 'clovers_9',
...        'diamons_7', 'clovers_8',
...        'diamons_10', 'clovers_10']
>>> three = list(sorted(lst, key=lambda i: int(i.partition('_')[2])))[:3]
>>> print(three)
['diamons_6', 'diamons_7', 'clovers_8']
>>>