面向對象高階-12迭代器實現原理

迭代器重溫

who 迭代器對象

必須有 __iter__,__next__ 這兩方法

__iter__

把對象轉化迭代器對象

__next__

迭代取值啦,運行一次取一個相對單位

案例:

• 列子一 --> 死循環

class Foo:
    def __init__(self, x):
        self.x = x

    def __iter__(self):
        return self

    def __next__(self):
        self.x += 1
        return self.x


f = Foo(3)
for i in f:
    print(i)

列子2 ---> StopIteration異常版

# 加上StopIteration異常
class Foo:
    def __init__(self, start, stop):
        self.num = start
        self.stop = stop

    def __iter__(self):
        return self

    def __next__(self):
        if self.num >= self.stop:
            raise StopIteration
        n = self.num
        self.num += 1
        return n

f = Foo(1, 5)

from collections import Iterable, Iterator
print(isinstance(f, Iterator))

for i in Foo(1, 5):
    print(i)

輸出結果:
True
1
2
3
4
列子3 ---> 模擬range

class Range:
    def __init__(self, n, stop, step):
        self.n = n
        self.stop = stop
        self.step = step

    def __next__(self):
        if self.n >= self.stop:
            raise StopIteration
        x = self.n
        self.n += self.step
        return x

    def __iter__(self):
        return self

for i in Range(1, 7, 3):
    print(i)

輸出結果
1
4
列子4 ---> 斐波那契數列實現

class Fib:
    def __init__(self):
        self._a = 0
        self._b = 1

    def __iter__(self):
        return self

    def __next__(self):
        self._a, self._b = self._b, self._a + self._b
        return self._a


f1 = Fib()

for i in f1:
    if i > 100:
        break
    print('%s ' % i, end='')

輸出結果:
1 1 2 3 5 8 13 21 34 55 89