替代方法，与@jamylak的解决方案一样快，并且使用更多的pythonic：
from itertools import imapmax(imap(len, d))
查看比较：
$ python -m timeit -s "d = {'group 1': 1, 'group 1000': 0}" "len(max(d,key=len))"1000000 loops, best of 3: 0.538 usec per loop$ python -m timeit -s "d = {'group 1': 1, 'group 1000': 0}" "max(len(x) for x in d)"1000000 loops, best of 3: 0.7 usec per loop$ python -m timeit -s "d = {'group 1': 1, 'group 1000': 0}; from itertools import imap" "max(imap(len, d))"1000000 loops, best of 3: 0.557 usec per loop
