如何在Python中使用C风格的for循环？

for for range并没有给我一个实际for循环的灵活性.

i = 0
while i < 7:
    if someCondition(i):
        i = 5
    i += 1

但是在该循环中,continue语句将不会具有与C for循环中的continue语句相同的效果.如果你想继续按照它在C中的方式工作,你必须抛出一个try / finally语句：

i = 0
while i < 7:
    try:
        if someCondition(i):
            i = 5
        elif otherCondition(i):
            continue
        print 'i = %d' % i
    finally:
        i += 1

如你所见,这非常难看.你应该寻找更多的Pythonic方式来编写你的循环.

UPDATE

这刚刚发生在我身上……有一个复杂的答案让你像C风格的循环一样使用普通的Python for循环,并允许通过编写自定义迭代器来更新循环变量.我不会为任何真正的程序推荐这个解决方案,但这是一个有趣的练习.

循环示例“C风格”：

for i in forrange(10):
    print(i)
    if i == 3:
        i.update(7)

输出：

0
1
2
3
8
9

诀窍是forrange使用int的子类来添加更新方法. forrange的实现：

class forrange:

    def __init__(self, startOrStop, stop=None, step=1):
        if step == 0:
            raise ValueError('forrange step argument must not be zero')
        if not isinstance(startOrStop, int):
            raise TypeError('forrange startOrStop argument must be an int')
        if stop is not None and not isinstance(stop, int):
            raise TypeError('forrange stop argument must be an int')

        if stop is None:
            self.start = 0
            self.stop = startOrStop
            self.step = step
        else:
            self.start = startOrStop
            self.stop = stop
            self.step = step

    def __iter__(self):
        return self.foriterator(self.start, self.stop, self.step)

    class foriterator:

        def __init__(self, start, stop, step):
            self.currentValue = None
            self.nextValue = start
            self.stop = stop
            self.step = step

        def __iter__(self): return self

        def next(self):
            if self.step > 0 and self.nextValue >= self.stop:
                raise StopIteration
            if self.step < 0 and self.nextValue <= self.stop:
                raise StopIteration
            self.currentValue = forrange.forvalue(self.nextValue, self)
            self.nextValue += self.step
            return self.currentValue

    class forvalue(int):
        def __new__(cls, value, iterator):
            value = super(forrange.forvalue, cls).__new__(cls, value)
            value.iterator = iterator
            return value

        def update(self, value):
            if not isinstance(self, int):
                raise TypeError('forvalue.update value must be an int')
            if self == self.iterator.currentValue:
                self.iterator.nextValue = value + self.iterator.step