yield

x='dddd'
print x
print type(x)
def fun1(Str):
   yield Str
y=fun1('123')
print y
print type(y)


C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/mycompany/Django/a36.py
dddd
<type 'str'>
<generator object fun1 at 0x0258F490>
<type 'generator'>

--------------------------------------------------------------------------------------

x='dddd'
print x
print type(x)
def fun1(Str):
   return Str
y=fun1('123')
print y
print type(y)


C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/mycompany/Django/a36.py
dddd
<type 'str'>
123
<type 'str'>

Process finished with exit code 0




def frange(start, stop, increment):
   x = start
   while x < stop:
    yield x
    x += increment
b= frange(0, 4, 0.5)
print b
print type(b)

def frange(start, stop, increment):
   x = start
   while x < stop:
    yield x
    x += increment
b= frange(0, 4, 0.5)
print b
print type(b)


C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/mycompany/Django/a36.py
dddd
<type 'str'>
<generator object fun1 at 0x0248F490>
<type 'generator'>


一个函数中需要有一个  yield 语句即可将其转换为一个生成器。 跟普通函数不同的是，
生成器只能用于迭代操作。 下面是一个实验，向你展示这样的函数底层工作机制


def countdown(n):
   print('Starting to count from', n)
   while n > 0:
   yield n
   n -= 1
   print('Done!')
 # Create the generator, notice no output appears
c=countdown(10)
print c
pritn type(c)


C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/mycompany/Django/a36.py
dddd
<type 'str'>
<generator object fun1 at 0x024CF490>
<type 'generator'>


--------------------------------------------------------------------------------------------
def countdown(n):
   print('Starting to count from', n)
   while n > 0:
     yield n
     n -= 1
   print('Done!')
# Create the generator, notice no output appears
c=countdown(3)
print c
print type(c)
print next(c)
print next(c)
print next(c)

C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/mycompany/Django/a38.py
<generator object countdown at 0x025EF4E0>
<type 'generator'>
('Starting to count from', 3)
3
2
1



如果改为return:

def countdown(n):
   print('Starting to count from', n)
   while n > 0:
     return n
     n -= 1
   print('Done!')
# Create the generator, notice no output appears
c=countdown(3)
print c
print type(c)
print next(c)
# print next(c)
# print next(c)

C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/mycompany/Django/a38.py
('Starting to count from', 3)
3
<type 'int'>
Traceback (most recent call last):
  File "C:/Users/TLCB/PycharmProjects/untitled/mycompany/Django/a38.py", line 11, in <module>
    print next(c)
TypeError: int object is not an iterator

Process finished with exit code 1

一个生成器函数主要特征是它只会回应在迭代中使用到的 next 操作。 一旦生成器函数返
回退出，迭代终止。我们在迭代中通常使用的for语句会自动处理这些细节，所以你无需
担心。