python基础-生成器进阶(send、from)、各种推导式、生成器表达式

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yield回顾

def cloth():for i in range(10):yield  '衣服%s'%ig = cloth()
for i in g:print(i)g = cloth()
for i in range(10):print(g.__next__())g = cloth()
lst = list(g)
for  i in lst:print(i)def method():yield 2,3,4y = method()
for i in y.__next__():print(i)

输出如下：

E:\python\python_sdk\python.exe E:/python/py_pro/2生成器函数.py
衣服0
衣服1
衣服2
衣服3
衣服4
衣服0
衣服1
衣服2
衣服3
衣服4
衣服0
衣服1
衣服2
衣服3
衣服42
3
4

send

def func():print('*'*10)a = yield 5print('a : ',a)yield 10
g = func()
num = g.__next__()
print(num)
num = g.__next__()
print(num)

输出如下：

E:\python\python_sdk\python.exe E:/python/py_pro/2生成器函数.py
**********
5
a :  None
10

我们看结果a:None是没有输出内容，是因为我们需要引入一个方法send
我们修改下代码如下：

def func():print('*'*10)a = yield 5print('a : ',a)yield 10
g = func()
num = g.__next__()
print(num)num2 = g.send('alex')
print(num2)

输出如下

E:\python\python_sdk\python.exe E:/python/py_pro/2生成器函数.py
**********
5
a :  alex
10

从哪一个yield开始接着执行，就把一个值传给了那个yield
send不能用在第一个触发生成器
生成器函数中有多少个yield就必须有多少个next+send

生成器结合装饰器

生成器的预激装饰器

def init(func):  #生成器的预激装饰器def inner(*args,**kwargs):g = func(*args,**kwargs)   #func = averagerprint(g.__next__())return greturn inner@init
def averager():term = yield 0print(term)yield 1g_avg = averager()
print(g_avg.send(19))

输出如下：

E:\python\python_sdk\python.exe E:/python/py_pro/2生成器函数.py
0
19
1

yield from

我们来看下面的一个错误的例子

def func():a = 1yield from ag = func()
print(g.__next__())

错误日志如下：

  File "E:/python/py_pro/2生成器函数.py", line 18, in <module>print(g.__next__())File "E:/python/py_pro/2生成器函数.py", line 14, in funcyield from a
TypeError: 'int' object is not iterable

说明是必须可以迭代的

def func():a = "safly"yield from ag = func()
for i in g:print(i)

输出如下：

s
a
f
l
y

当然其他的元组、列表也是可以的

print("-------列表-----")
def func():a = [1,2,3]yield from ag = func()
print(g.__next__())
print(g.__next__())
print(g.__next__())
print("-------元组-----")
def func():a = (1,2,3)yield from a
g = func()
for i in g:print(i)print("-------字典-----")
def func():a = {"a":1,"b":2}yield from ag = func()
for i in g:print(i)
print("-------组合-----")
def func():a = 'AB'b = [1,2]yield from ayield from by = func()
print(y.__next__())
print(y.__next__())
print(y.__next__())
print(y.__next__())

输出如下：

E:\python\python_sdk\python.exe E:/python/py_pro/2生成器函数.py
-------列表-----
1
2
3
-------元组-----
1
2
3
-------字典-----
a
b
-------组合-----
A
B
1
2Process finished with exit code 0

列表推导式

y = [1,2,3,4,5,6,7,8]
x = [i*i for i in y]
print(x)x2 = [i/2 for i in range(10)]
print(x2)

输出如下：

E:\python\python_sdk\python.exe E:/python/py_pro/3生成器表达式.py
[1, 4, 9, 16, 25, 36, 49, 64]
[0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5]

继续看列表推导式带if条件的

print(list(range(0,30,3)))
print([i for i in range(30) if i%3 == 0])

输出如下：

[0, 3, 6, 9, 12, 15, 18, 21, 24, 27]
[0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

字典推导式

mcase = {'a': 10, 'b': 34}
mcase_frequency = {mcase[k]:k for k in mcase}
print(mcase_frequency)mcase = {'a': 10, 'b': 34, 'A': 7, 'Z': 3}
mcase_frequency = {k.lower(): (mcase.get(k.lower(), 0) + mcase.get(k.upper(), 0)) for k in mcase}
print(mcase_frequency)

输出如下：

E:\python\python_sdk\python.exe E:/python/py_pro/4各种推导式扩展.py
{10: 'a', 34: 'b'}
{'a': 17, 'b': 34, 'z': 3}

集合推导式

squared = {x**2 for x in [1, -1, 2]}   #{1,4}
print(squared)

输出如下：

E:\python\python_sdk\python.exe E:/python/py_pro/4各种推导式扩展.py
{1, 4}

生成器表达式

y = [1,2,4]
g = (i*i for i in y)
print(g)
print(list(g))y = [1,2,4]
g = (i*i for i in y)
for i in g:print(i)

输出如下：

E:\python\python_sdk\python.exe E:/python/py_pro/3生成器表达式.py
<generator object <genexpr> at 0x03116240>
[1, 4, 16]
1
4
16

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