python字典元组和集合

字典的内置函数

1.sorted 排序，让字典的数据按照顺序输出

found = {'a':0,'u':2,'i':0}

for keys in found:
    print(keys)   #a u i


for keys in sorted(found):
    print(keys)    # a i u

2.items，返回一个键值对列表

found = {'a':0,'u':2,'i':0}

for keys in found:
    print(keys)   #a u i

for keys,values in found.items():
    print("keys = {} and values ={}".format(keys,values))
    # keys = a and values =0
    # keys = u and values =2
    # keys = i and values =0

for keys,values in sorted(found.items()):
    print("keys = {} and values ={}".format(keys,values))
    # keys = a and values =0
    # keys = i and values =0
    # keys = u and values =2

3.字典初始化函数 setdefault

fruits = ['apples','bananas','pears']
found = {'apples':2,'pears':3}

for fruit in fruits:
    if fruit in found:
        found[fruit] += 1
    else:
        found[fruit] = 1
    print('{}个数为{}'.format(fruit,found[fruit]))


# 等价于：
for fruit in fruits:
    found.setdefault(fruit,0)
    found[fruit] += 1
    print('{}个数为{}'.format(fruit,found[fruit]))

集合

特性：不重复，无序

1.union合并集合，将集合A和B合并，去重后创建一个新集合

vowels = set('aeiou')

print(vowels)  #{'i', 'a', 'u', 'o', 'e'}

word = 'hello'

u = vowels.union(set(word))   #{'o', 'i', 'u', 'e', 'h', 'a', 'l'}

2.difference，给定两个集合，告诉你哪些元素只在集合A中存在而不在集合B中存在

vowels = set('aeiou')

print(vowels)  #{'i', 'a', 'u', 'o', 'e'}

word = 'hello'

l = vowels.difference(set(word))    #{'u', 'a', 'i'}

3.intersection报告共同元素，即集合A和集合B的共同元素

vowels = set('aeiou')

print(vowels)  #{'i', 'a', 'u', 'o', 'e'}

word = 'hello'

i = vowels.intersection(set(word))   #{'o', 'e'}

元祖

特性：不可变

优势：提供性能，避免不必要的开销

创建规则：特例

只有一个对象的元祖，创建时需要在末尾加上，

t = ('python')
print(type(t))   #<class 'str'>
print(t)    #python

s = ('python',)
print(type(s))    #<class 'tuple'>
print(s)    #('python',)