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from typing import Generic
from typing import Iterable
from typing import Iterator
from typing import List
from typing import TypeVar
T = TypeVar("T")
class CachedIterable(Iterable[T], Generic[T]):
"""
A cache-implementing wrapper for an iterator.
Note that this is class is `Iterable[T]` rather than `Iterator[T]`.
It should not be iterated by his own.
"""
cache: List[T]
iter: Iterator[T]
completed: bool
def __init__(self, it: Iterator[T]):
self.iter = iter(it)
self.cache = list()
self.completed = False
def __iter__(self) -> Iterator[T]:
return CachedIterator(self)
def __next__(self) -> T:
try:
item = next(self.iter)
except StopIteration:
self.completed = True
raise
else:
self.cache.append(item)
return item
def __del__(self) -> None:
del self.cache
class CachedIterator(Iterator[T], Generic[T]):
"""
A cache-using wrapper for an iterator.
This class is only constructed by `CachedIterable` and cannot be used without it.
"""
parent: CachedIterable[T]
position: int
def __init__(self, parent: CachedIterable[T]):
self.parent = parent
self.position = 0
def __next__(self) -> T:
if self.position < len(self.parent.cache):
item = self.parent.cache[self.position]
elif self.parent.completed:
raise StopIteration
else:
item = next(self.parent)
self.position += 1
return item
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