https://www.cnblogs.com/itdyb/p/5731804.html
请注意python3 return 的是迭代器 python2返回的是列表
>>> ls=[1,2,3]
>>> dst=map(str,ls)
>>> print(dst)
<map object at 0x7f08828b5da0>
>>> print( list(dst) )
['1', '2', '3']
http://www.runoob.com/python/python-func-map.html
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