python基础

寻找差异

li1=set([1,2,3,4])
li2=set([4,5,6,7])

update_set=li1.intersection(li2)
delete_set=li1.symmetric_difference(update_set)
add_set=li2.symmetric_difference(update_set)

print("update_set:", update_set)
print("delete_set:", delete_set)
print("add_set:", add_set)

li3=li1.difference(li2)
print("li3:",li3)

li4=li1.symmetric_difference(li2)
print("li4:",li4)

update_set: {4}
delete_set: {1, 2, 3}
add_set: {5, 6, 7}
li3: {1, 2, 3}
li4: {1, 2, 3, 5, 6, 7}

计数器
import collections

obj=collections.Counter('aaaaabbbbcccddeffgg')
ret=obj.most_common(4)

print('obj:',obj)
print('ret:',ret)

for k in obj.elements():
    print(k)

for k,v in obj.items():
    print(k,v)

obj: Counter({'a': 5, 'b': 4, 'c': 3, 'd': 2, 'f': 2, 'g': 2, 'e': 1})
ret: [('a', 5), ('b', 4), ('c', 3), ('d', 2)]
a
a
a
a
a
b
b
b
b
c
c
c
d
d
e
f
f
g
g
a 5
b 4
c 3
d 2
e 1
f 2
g 2

有序字典
import collections

dic=collections.OrderedDict()
dic['k1']='v1'
dic['k2']='v2'
dic['k3']='v3'

print(dic)

OrderedDict([('k1', 'v1'), ('k2', 'v2'), ('k3', 'v3')])


默认字典

import collections

dic=collections.defaultdict(list)
dic['k1'].append('alex')
print(dic)

defaultdict(<class 'list'>, {'k1': ['alex']})