python3-列表推导的使用

1.列表推导式列表推导能非常简洁的构成一个新列表：只用一条简洁的表达式即可对得到的元素进行转换变形。

　　　格式：[表达式 for 变量 in 列表]或[表达式 for 变量 in 列表 if 条件]

 

>>> list =[x*x for x in range(10)]
相当于
>>> alist= []
>>> for x in range(10):
也相当于
>>> list= list(map(lambda x:x*x,range(10)))

 

 2.使用列表推导式实现嵌套列表的平铺

 

>>> vec=[[1,2,3],[4,5,6],[7,8,9]]
>>> [num for elem in vec for num in elem]
[1, 2, 3, 4, 5, 6, 7, 8, 9]
相当于
>>> vec=[[1,2,3],[4,5,6],[7,8,9]]
>>> result =[]
>>> for elem in vec:
    　　for num in elem:
    　　result.append(num)
>>> result
[1，2，3，4，5，6，7，8，9]

 

 3.已知有一个包含一些同学成绩的字典，计算成绩的最高分、最低分、平均分，并查找所有最高分同学。

 

>>> scores={"zhangsan":45,"lisi":78,"wangwu":40,"zhouliu":96,"zhaoqi":65,"sunba":90,"zhengjiu":78,"wushi":99,"dongshiyi":60}
>>> heighest=max(scores.values())
>>> lowest = min(scores.values())>>> average=sum(scores.values())*1.0/len(scores)
>>> heighest,lowest,average
(99, 40, 72.33333333333333)
>>> heighestPerson=[name for name,score in scores.items()if score == heighest]
>>> heighestPerson
['wushi']

 

 4.在列表推导式中使用多个循环，实现多序列元素组合，并且可以结合条件语句过滤特定元素

 

>>> [(x,y)for x in range(3) for y in range(2)]
[(0, 0), (0, 1), (1, 0), (1, 1), (2, 0), (2, 1)]
>>> [(x,y) for x in [1,2,3]for y in [3,1,4]if x!=y]
[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]