'''普通函数'''
def func():
print(111)
return 222
ret = func() # 111
print(ret) # 222
111
222
'''函数中含有yield就是生成器'''
def func():
print(111)
yield 222
gen = func()
print(gen) # <generator object func at 0x0000000006085D00>
ret1 = gen.__next__() # 111
print(ret1) # 222
<generator object func at 0x0000000007A8BB48>
111
222
def func():
print(111)
yield 22
print(333)
yield 444
gen = func()
ret = gen.__next__() # 111
print(ret) # 22
ret2 = gen.__next__() # 333
print(ret2) # 444
ret3 = gen.__next__() # StopIteration: # 值取空，就报StopIteration
print(ret3)
---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
<ipython-input-25-9050db3134ee> in <module>()
10 ret2 = gen.__next__()
11 print(ret2)
---> 12 ret3 = gen.__next__()
13 print(ret3)
StopIteration:
'''send和__next__()区别
1.send和next()都是让生成器向下走一次
2.send可以给上一个yield的位置传递值，不能给最后一个yield发送值，在第一次执行生成器代码的时候不能使用send()
'''
def func():
print(111)
a = yield "aaa"
print("a = ", a)
b = yield "bbb"
print("b = ", b)
c = yield "ccc"
print("c = ", c)
yield "Bye"
gen = func()
print(gen.__next__()) # 111 aaa
print(gen.__next__()) # a = None bbb
print(gen.__next__()) # b = None ccc
print(gen.__next__()) # c = None Bye
print(gen.__next__()) # StopIteration
111
aaa
a = None
bbb
b = None
ccc
c = None
Bye
---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
<ipython-input-26-e1ddf9d0af94> in <module>()
14 print(gen.__next__()) # b = bbb ccc
15 print(gen.__next__()) # c = ccc Bye
---> 16 print(gen.__next__()) # StopIteration
StopIteration:
def func():
print(111)
a = yield "aaa"
print("a = ", a)
b = yield "bbb"
print("b = ", b)
c = yield "ccc"
print("c = ", c)
yield "Bye"
gen = func()
print(gen.__next__()) # 111 aaa
ret1 = gen.send("apple") # a = apple
print(ret1) # bbb
ret2 = gen.send("banana") # b = banana
print(ret2) # ccc
ret3 = gen.send("orange") # c = orange
print(ret3) # Bye
ret4 = gen.send("pear") # StopIteration
111
aaa
a = apple
bbb
b = banana
ccc
c = orange
Bye
---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
<ipython-input-27-3a8a2fe89824> in <module>()
17 ret3 = gen.send("orange") # c = orange
18 print(ret3) # Bye
---> 19 ret4 = gen.send("pear") # StopIteration
StopIteration:
'''生成器可以使用for循环去内部的元素'''
def func():
print(111)
yield 222
print(333)
yield 444
print(555)
yield 666
gen = func()
for i in gen:
print(i)
111
222
333
444
555
666
'''yield在循环体内'''
def func(n):
print("start...")
count = 0
while count < n:
count += 1
yield count
print("end...")
g = func(5)
for i in g: #for循环本质就是next下一个元素
print(i)
返回结果:
start...
1
2
3
4
5
end...
'''注意区分send()给上一个yield位置传递一个值,yield是向外返回一个值'''
def func():
print("apple")
y1 = yield 2
print(y1, " = banana")
y2 = yield 1
print(y2, " = orange")
y3 = yield 3
print(y3)
g = func()
print(g.__next__())
print(next(g))
print(g.send("big"))
返回结果:
apple
2
None = banana
1
big = orange
3
'''生成器表达式(结果 for循环 if语句)'''
# lst = [i*i for i in range(5)]
# print(lst) #列表生成式,直接生成一个列表,下面把中括号换为小括号,就是一个生成器
# g = (i*i for i in range(5))
# print(g) #生成器对象,省内存
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g)) #StopIteration
'''yield from是将列表中的每一个元素返回'''
def gen():
lst = ["apple", "banana", "pear", "orange"]
yield from lst
g = gen()
for i in g:
print(i)
apple
banana
pear
orange
def gen():
lst = ["apple", "banana", "orange", "pear"]
lst2 = ["peach", "watermelon", "strawberry", "blueberry"]
yield from lst
yield from lst2
g = gen()
print(list(g)) # ['apple', 'banana', 'orange', 'pear', 'peach', 'watermelon', 'strawberry', 'blueberry']
['apple', 'banana', 'orange', 'pear', 'peach', 'watermelon', 'strawberry', 'blueberry']
'''
一个面试题,难度系数50000000000颗星
'''
# def add(a, b):
# return a + b
#
# def test():
# for r_i in range(4):
# yield r_i
#
# g = test() #g是一个生成器,也是一个迭代器
#
# for n in [2, 10]:
# g = (add(n, i) for i in g)
#
# print(list(g))
'''
分析,当n=2时, g = (add(n, i) for i in g) 右边是一个生成器表达式, g就是一个生成器
当n=10时, g = (add(n, i) for i in (add(n, i) for i in g)) 右边是一个生成器表达式, g就是一个生成器
当程序执行到list(g)时,开始取生成器里的值
当n=10时,g = (add(10, i) for i in (add(10, i) for i in g))
g = (add(10, i) for i in (10, 11, 12, 13))
g = (20, 21, 22, 23)
所以打印出来的值就是[20, 21, 22, 23]
'''
