What is the result of a yield expression in Python?
I know that yield turns a function into a generator, but what is the return value of the yield expression itself? For example:
def whizbang():
for i in range(10):
x = yield i
What is the value of variable x as this function executes?
I've read the Python documentation: http://docs.python.org/reference/simple_stmts.html#grammar-token-yield_stmt and there seems to be no mention of the value of the yield expression itself.
You can also send values to generators. If no value is sent then x is None , otherwise x takes on the sent value. Here is some info: http://docs.python.org/whatsnew/2.5.html#pep-342-new-generator-features
>>> def whizbang():
for i in range(10):
x = yield i
print 'got sent:', x
>>> i = whizbang()
>>> next(i)
0
>>> next(i)
got sent: None
1
>>> i.send("hi")
got sent: hi
2
Here is an example of yield to give buffered output from say a big cahce
#Yeild
def a_big_cache():
mystr= []
for i in xrange(100):
mystr.append("{}".format(i))
return mystr
my_fat_cache = a_big_cache()
def get_in_chunks(next_chunk_size):
output =[]
counter = 0
for element in my_fat_cache:
counter += 1
output.append(element)
if counter == next_chunk_size:
counter = next_chunk_size
next_chunk_size+= next_chunk_size
yield output
del output[:]
r = get_in_chunks(10)
print next(r)
print next(r)
Output is
['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
['10', '11', '12',> '13', '14', '15', '16', '17', '18', '19']
这段代码会产生一些输出
def test():
for i in range(10):
x = yield i
t = test()
for i in test():
print i