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from typing import Iterator, Optional, TypeVar
__all__ = [
'PeekableIterator',
]
T = TypeVar('T')
class PeekableIterator(Iterator[T]):
_inner: Iterator[T]
_peeked: Optional[T]
def __init__(self, inner: Iterator[T]):
self._inner = inner
self._peeked = None
def __iter__(self) -> Iterator[T]:
return self
def __next__(self) -> T:
if self._peeked is not None:
result = self._peeked
self._peeked = None
return result
return next(self._inner)
def peek(self) -> T:
if self._peeked is None:
self._peeked = next(self._inner)
return self._peeked
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