بروتوكول المكرّر

ما المقصود بالتكرار؟

for ch in 'abc':
    print(ch)

iter() وnext()

it = iter([10, 20, 30])
print(next(it))
print(next(it))
print(next(it))

StopIteration

it = iter([1])
print(next(it))
try:
    next(it)
except StopIteration:
    print('No more items')

طريقتا Dunder

class Count:
    def __init__(self, n):
        self.i = 0
        self.n = n
    def __iter__(self):
        return self
    def __next__(self):
        if self.i >= self.n:
            raise StopIteration
        self.i += 1
        return self.i

for x in Count(3):
    print(x)

القابل للتكرار مقابل المكرّر

nums = [1, 2, 3]
print(iter(nums) is iter(nums))
it = iter(nums)
print(it is iter(it))

يُستنفد المكرّر مرة واحدة

it = iter([1, 2])
print(list(it))
print(list(it))

مكرّر شبيه بـ Range

class EvenUpTo:
    def __init__(self, limit):
        self.cur = 0
        self.limit = limit
    def __iter__(self):
        return self
    def __next__(self):
        if self.cur > self.limit:
            raise StopIteration
        value = self.cur
        self.cur += 2
        return value

print(list(EvenUpTo(8)))

فصل الكائن القابل للتكرار عن المكرّر

class Bag:
    def __init__(self, items):
        self.items = items
    def __iter__(self):
        return BagIterator(self.items)

class BagIterator:
    def __init__(self, items):
        self.items = items
        self.i = 0
    def __iter__(self):
        return self
    def __next__(self):
        if self.i >= len(self.items):
            raise StopIteration
        v = self.items[self.i]
        self.i += 1
        return v

b = Bag(['x', 'y'])
print(list(b))
print(list(b))

استخدام next() مع قيمة افتراضية

it = iter([42])
print(next(it, 'done'))
print(next(it, 'done'))

المكرّرات موفرة للذاكرة

class Naturals:
    def __init__(self):
        self.n = 0
    def __iter__(self):
        return self
    def __next__(self):
        self.n += 1
        return self.n

it = iter(Naturals())
print(next(it), next(it), next(it))

الدوال المضمّنة التي تستهلك المكرّرات

class Count:
    def __init__(self, n):
        self.i = 0
        self.n = n
    def __iter__(self):
        return self
    def __next__(self):
        if self.i >= self.n:
            raise StopIteration
        self.i += 1
        return self.i

print(sum(Count(5)))
print(max(Count(5)))

اختبار سريع

مراجعة