yield和yield from的用法示例

# the examples of yield and yield from syntax

def accumulate():
    tally = 0
    print('accumulate before while')
    while True:
        print('accumulate before yield')
        next = yield
        print('accumulate after yield , next = {0}'.format(next))
        if next is None:
            return tally
        tally += next

def gather_tallies(tallies):
    print('gather before while')
    while True:
        print('gather before yield')
        tally = yield from accumulate()
        print('gather after yield tally = {0}'.format(tally))
        tallies.append(tally)

tallies = []
acc = gather_tallies(tallies)
print('before next')
next(acc)
print('after next')
print('before send')
for i in range(4):
    acc.send(i)
print('after send')
print('before send none')
acc.send(None)
print('after send none')

for i in range(5):
    acc.send(i)
acc.send(None)
print(tallies)

运行结果如下：

[Cambox@laptop ~]$ python34 python-test/test.py
before next
gather before while
gather before yield
accumulate before while
accumulate before yield
after next
before send
accumulate after yield , next = 0
accumulate before yield
accumulate after yield , next = 1
accumulate before yield
accumulate after yield , next = 2
accumulate before yield
accumulate after yield , next = 3
accumulate before yield
after send
before send none
accumulate after yield , next = None
gather after yield tally = 6
gather before yield
accumulate before while
accumulate before yield
after send none
accumulate after yield , next = 0
accumulate before yield
accumulate after yield , next = 1
accumulate before yield
accumulate after yield , next = 2
accumulate before yield
accumulate after yield , next = 3
accumulate before yield
accumulate after yield , next = 4
accumulate before yield
accumulate after yield , next = None
gather after yield tally = 10
gather before yield
accumulate before while
accumulate before yield
[6, 10]