python中的OrderedDict

该类型存放顺序和添加顺序一致,比如逐个赋值,但和dict直接转化过去的顺序不一定一样.

d1 = collections.OrderedDict()

d1['b'] = 'B'
d1['a'] = 'A'
d1['c'] = 'C'
d1['2'] = '2'
d1['1'] = '1'

# OrderedDict([('b', 'B'), ('a', 'A'), ('c', 'C'), ('2', '2'), ('1', '1')])

dict1 = {"1": 1, "2":2, '3':3} 
print(dict1)
od1 = OrderedDict(dict1) # 和dict1初始化时看到的顺序不一定一样,但和dict1打印出来的顺序一致
print(od1)

#{'3': 3, '2': 2, '1': 1}
#OrderedDict([('3', 3), ('2', 2), ('1', 1)])

将OrderedDict转化为dict:

list_key = []
list_value = []
# OrderedDict转成dict
for key in od1.keys():
    list_key.append(key)
for value in od1.values():
    list_value.append(value)
zip_od = zip(list_key, list_value)
dict_od = dict(zip_od)
print(dict_od)

对该类型可以进行排序操作.

dd = {'banana': 3, 'apple':4, 'pear': 1, 'orange': 2}

#按key排序
kd = collections.OrderedDict(sorted(dd.items(), key=lambda t: t[0])) 
print kd
#按照value排序
vd = collections.OrderedDict(sorted(dd.items(),key=lambda t:t[1]))
print vd

#输出
OrderedDict([('apple', 4), ('banana', 3), ('orange', 2), ('pear', 1)])
OrderedDict([('pear', 1), ('orange', 2), ('banana', 3), ('apple', 4)])

下面这种排序效果起不到作用:

sorted_od = (sorted(d1, key=lambda t: t[0]))
#['1', '2', 'a', 'b', 'c']

因为:
for i in d1:
    print(i)
# b
# a
# c
# 2
# 1

for j in d1.items():
    print(j)
# ('b', 'B')
# ('a', 'A')
# ('c', 'C')
# ('2', '2')
# ('1', '1')