#列表推导式：

egg_list = []
for i in range(10):
    egg_list.append(‘鸡蛋%s‘%i)
print(egg_list)



egon
egg_list=[‘鸡蛋%s‘%i for i in range(10)]    #列表推导式
print(egg_list)

# print([i*i for i in range(10)])

#生成器表达式

g = (i for i in range(10))
print(g)
for i in  g:
    print(i)

# 括号不一样
# 返回的值不一样 === 几乎不占用内存

老母鸡=(‘鸡蛋%s‘%i for i in range(10))   #生成器表达式
print(老母鸡)
for 蛋 in 老母鸡:
    print(蛋)


#g = (i*i for i in range(10))
#print(g.__next__())

#[每一个元素或者是和元素相关的操作 for 元素 in 可迭代数据类型]    #遍历之后挨个处理
#[满足条件的元素相关的操作 for 元素 in 可迭代数据类型 if 元素相关的条件]   #筛选功能

# #30以内所有能被3整除的数
ret = [i for i in range(30) if i%3 == 0]  #完整的列表推导式
g = (i for i in range(30) if i%3 == 0)  #完整的生成器表达式
print(ret)

# #30以内所有能被3整除的数的平方
ret = [i*i for i in (1,2,3,4) if i%3 == 0] #元组推导式
ret = (i*i for i in range(30) if i%3 == 0)
print(ret)

# # 例三:找到嵌套列表中名字含有两个‘e’的所有名字
names = [[‘Tom‘, ‘Billy‘, ‘Jefferson‘, ‘Andrew‘, ‘Wesley‘, ‘Steven‘, ‘Joe‘],
         [‘Alice‘, ‘Jill‘, ‘Ana‘, ‘Wendy‘, ‘Jennifer‘, ‘Sherry‘, ‘Eva‘]]
ret1 = [name for lst in names for name in lst if name.count(‘e‘) ==2]
ret2 = (name for lst in names for name in lst if name.count(‘e‘) ==2)
print(ret1)

# 例一：将一个字典的key和value对调
mcase = {‘a‘: 10, ‘b‘: 34}
#{10:‘a‘ , 34:‘b‘}
mcase_frequency = {mcase[k]: k for k in mcase}
print(mcase_frequency)

# 例二：合并大小写对应的value值，将k统一成小写
mcase = {‘a‘: 10, ‘b‘: 34, ‘A‘: 7, ‘Z‘: 3}
#{‘a‘:10+7,‘b‘:34,‘z‘:3}
mcase_frequency = {k.lower(): mcase.get(k.lower(), 0) + mcase.get(k.upper(), 0) for k in mcase}
print(mcase_frequency)

d = {‘a‘: 10}

d[‘a‘] #10

# d[‘b‘] #报错

print(d.get(‘a‘)) #10

print(d.get(‘b‘)) #None

print(d.get(‘b‘, 0)) #0
    

squared = {x**2 for x in [1, -1, 2]}
print(squared)

#列表解析
sum([i for i in range(100000000)])#内存占用大,机器容易卡死
 
#生成器表达式
sum(i for i in range(100000000))#几乎不占内存