python一些东西

assert repr()

 >>> a
 ['d', 'c', 'c', 'f', 'a', 'a', 'b', 'c', 'd']
 >>> sorted(a)
 ['a', 'a', 'b', 'c', 'c', 'c', 'd', 'd', 'f']
 >>> from collections import Counter
 >>> a_counter = Counter(a)
 >>> a_counter
 Counter({'c': 3, 'd': 2, 'a': 2, 'f': 1, 'b': 1})
 >>> a_counter.update(["d","d"])
 >>> a_counter
 Counter({'d': 4, 'c': 3, 'a': 2, 'f': 1, 'b': 1})
 >>> type(a_counter)
 <class 'collections.Counter'>
 >>> a_counter.most_common(3)
 [('d', 4), ('c', 3), ('a', 2)]

 #round() 方法返回浮点数x的四舍五入值。

 round(70.23456) :  70
 round(56.659,1) :  56.7
 round(80.264, 2) :  80.26
 round(100.000056, 3) :  100.0
 round(-100.000056, 3) :  -100.0