Custom cache with iterator does not work as intended

I got the following class, where:

iterable is the passed argument, like for example range(20), n_max is an optional value, which limits the numbers of elements the cache should have, iterator is a field that gets initiated with the iterable, cache is the list I am trying to fill and finished is a bool which signals if the iterator is "empty" or not. Here is an example input:

>>> iterable = range(20)
>>> cachedtuple = CachedTuple(iterable)
>>> print(cachedtuple[0])
0
>>> print(len(cachedtuple.cache))
1
>>> print(cachedtuple[10])
10
>>> print(len(cachedtuple.cache))
11
>>> print(len(cachedtuple))
20
>>> print(len(cachedtuple.cache))
20
>>> print(cachedtuple[25])


@dataclass
class CachedTuple:
    iterable: Iterable = field(init=True)
    n_max: Optional[int] = None
    iterator: Iterator = field(init=False)
    cache: list = field(default_factory=list)
    finished: bool = False

    def __post_init__(self):
        self.iterator = iter(self.iterable)

    def cache_next(self):
        
        if self.n_max and self.n_max <= len(self.cache):
            self.finished = True
        else:
            try:
                nxt = next(self.iterator)
                self.cache.append(nxt)

            except StopIteration:
                self.finished = True


    def __getitem__(self, item: int):

        match item:
            case item if type(item) != int:
                raise IndexError

            case item if item < 0:
                raise IndexError

            case item if self.finished or self.n_max and item > self.n_max:
                raise IndexError(f"Index {item} out of range")

            case item if item >= len(self.cache):
                while item - len(self.cache) >= 0:
                    self.cache_next()

                return self.__getitem__(item)

            case item if item < len(self.cache):
                return self.cache[item]


    def __len__(self):

        while not self.finished:
            self.cache_next()
        return len(self.cache)

Although this code is certainly not good, at least it works for almost every scenario, but using the range function of Python for example. If I use for example

cachedtuple = CachedTuple(range(20))
for element in cachedtuple:
    print(element)

I get the element until 19 and then the program loops infinitely. I think one problem might be that I have no raise StopIteration in my code. So I am kind of lost how to fix this mess.

source https://stackoverflow.com/questions/70793606/custom-cache-with-iterator-does-not-work-as-intended