022_generator

#!/usr/bin/env python
# Author:liujun

# List Comprehensions
# A list comprehension generates all elements at once ,which consumes a lot of memory
# version 1
ls = [ i*2 for i in range(10) ]
print(ls)

# version 2
def func(i):
    return i*2 + 1
ls = [ func(i) for i in range(10)]
print(ls)



# list generator
# A list generator doesn't generate any elements, elements are generated only when they are accessed
lsg = (( func(i) for i in range(20)))
print(lsg) # You can not print lsg directly
# If you want to print lsg,do the following
for i in lsg:
   print(i)

lsg2 = (( func(i) for i in range(20)))
print(lsg2.__next__())
print(lsg2.__next__())
print(lsg2.__next__())
print(lsg2.__next__())
print(lsg2.__next__())
print(lsg2)




def fib(max):
    n, a, b = 0, 0, 1
    while n < max:
        yield b # b is the value you want to return.
        a,b = b,a+b
        n = n+1
f = fib(100)  #f is a generator
while True:
    try:
        x = next(f)
        print("f:",x)
    except StopIteration as e:
        print("Generator return value:",e.value)
        break




def consumer(name):
    print("%s is ready to eat buns"%(name))
    while True:
        baozi = yield
        print("bun [%s] is coming here and eaten by [%s]"%(baozi,name))

def producer(name):
    c = consumer("A")
    c2 = consumer("B")
    c.__next__()
    c2.__next__()

    print("I am starting to make buns")
    for i in range(10):
        c.send(name)
        c2.send(name)
producer("meat")