Python笔记2

列表推导式：

list=[num*num  for num in range(1,11) if num%2==0]
print(list) #[4, 16, 36, 64, 100]

list=[char+num for num in ['1','2','3'] for char in ['a','b','c']]
print(list) #拼接数字和字符   ['1a', '1b', '1c', '2a', '2b', '2c', '3a', '3b', '3c']

生成器表达式：
将列表推导式的方括号[]改为小括号（）即可创建一个生成器,通过next()调用算法实时生成元素，因此生成器占用的内存空间很小：
list=(num*num for num in range(1,11))
生成器函数：
yield关键字

def s(i):
  for n in range(i):
     print('before yield')
     yield n*n
     print('after yield')
for n in s(5):
     print(n)

 结果：

'''before yield
0
after yield
before yield
1
after yield
before yield
4
after yield
before yield
9
after yield
before yield
16
after yield'''

迭代器：