chapter5 函数进阶*3

生成器与迭代

##generator
#
L = [x*x for x in range(10)]
g = (x*x for x in range(10))
print(L)
print(g)

print(next(g))

for n in g:
    print(n)

def fib(max):
    n, a, b = 0, 0, 1
    while n < max:
        print(b)
        a, b = b , a+b
        n += 1
    return 'done'

fib(10)

def fib(max):
    n, a, b = 0, 0, 1
    while n < max:
        yield b
        a, b, = b, a+b
        n += 1
    return 'done'

f = fib(10)
print(f)

def odd():
    print('step 1')
    yield 1
    print('step 2')
    yield(3)
    print('step 3')
    yield(5)

o = odd()
next(o)
next(o)
next(o)

##用生成器写杨辉三角
def triangles():
    L = [1]
    while 1:
        yield L
        temp = [1]
        for i in range(len(L)-1):
            temp.append(L[i] + L[i+1])
        temp.append(1)
        L = temp[:]

gen_list = triangles()
print(next(gen_list))
print(next(gen_list))
print(next(gen_list))
print(next(gen_list))
print(next(gen_list))
print(next(gen_list))

n = 0
results = []
for t in triangles():
    print(t)
    results.append(t)
    n += 1
    if n == 10:
        break

print(results)

##更好的写法
def triangles_better():
    L = [1]
    while 1:
        yield L
        L = [L[i]+L[i+1] for i in range(len(L)-1)]
        L.insert(0, 1)
        L.append(1)

def triangles_better_2():
    L = [1]
    while 1:
        yield L
                L.append(0)
        L = [L[i]+L[i-1] for i in range(len(L))]


better_list = triangles_better()
print(next(better_list))
print(next(better_list))
print(next(better_list))
print(next(better_list))
print(next(better_list))
print(next(better_list))
print(next(better_list))


##Iterator
#

from collections import Iterable
print(isinstance([], Iterable))
print(isinstance({}, Iterable))
print(isinstance('abc', Iterable))
print(isinstance((x for x in range(10)), Iterable))

from collections import Iterator
print(isinstance((x for x in range(10)), Iterator))
print(isinstance([], Iterator))
print(isinstance({}, Iterator))
print(isinstance('abc', Iterator))

##生成器都是Iterator对象，但list、dict、str虽然是Iterable，却不是Iterator。

print(isinstance(iter('abc'), Iterator))


L = [1, 2, 3, 4]
I = iter(L)
print(next(I))
print(next(I))
print(next(I))
print(next(I))
##StopIteration
print(next(I))