构造字典

有一个列表values=[1,3,5,7,9,12,56,98,23,77,67,87,99,4,3,43,54,23],请构造一个字典，当值小于50时key为small，当值大于等于50时key为big。

方法一：

dic = {}   #定义一个空的字典
values=[1,3,5,7,9,12,56,98,23,77,67,87,99,4,3,43,54,23]
for i in values:       #对字典进行遍历
    if i < 50 :
        if ‘small‘ in dic.keys():       #判断small这个key是否在字典中
            dic[‘small‘].append(i)      
        else:
            dic[‘small‘]=[i]            
    else:
        if ‘big‘ in dic.keys():
            dic[‘big‘].append(i)
        else:
            dic[‘big‘]=[i]
print("The new dictionary is %s" % dic)

The new dictionary is {‘small‘: [1, 3, 5, 7, 9, 12, 23, 4, 3, 43, 23], ‘big‘: [56, 98, 77, 67, 87, 99, 54]}

方法二：

import collections
dic = collections.defaultdict(list)   #定义一个字典，默认是列表
values=[1,3,5,7,9,12,56,98,23,77,67,87,99,4,3,43,54,23]
for i in values:
    if i < 50:
        dic[‘small‘].append(i)
    else:
        dic[‘big‘].append(i)
print("The new dictionary is %s" % dic)

The new dictionary is defaultdict(<class ‘list‘>, {‘small‘: [1, 3, 5, 7, 9, 12, 23, 4, 3, 43, 23], ‘big‘: [56, 98, 77, 67, 87, 99, 54]})

以上两种方法仅供参考，有需要的朋友可以看一下，共同探讨共同进步。

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构造字典

原文：http://www.cnblogs.com/winter1519/p/7019914.html