139.py

"""
Problem:

Given an iterator with methods next() and hasNext(), create a wrapper iterator,
PeekableInterface, which also implements peek(). peek shows the next element that would
be returned on next().

Here is the interface:

class PeekableInterface(object):
    def __init__(self, iterator):
        pass

    def peek(self):
        pass

    def next(self):
        pass

    def hasNext(self):
        pass
"""

from typing import Any, Iterable


class PeekableInterface(object):
    def __init__(self, iterator: Iterable[Any]) -> None:
        self.iterator = iterator
        try:
            self.next_val = next(self.iterator)
            self.has_next = True
        except StopIteration:
            self.next_val = None
            self.has_next = False

    def peek(self) -> Any:
        return self.next_val

    def next(self) -> Any:
        if self.has_next:
            curr_elem = self.next_val
            try:
                self.next_val = next(self.iterator)
            except StopIteration:
                self.next_val = None
                self.has_next = False
            return curr_elem
        return None

    def hasNext(self) -> bool:
        return self.has_next


if __name__ == "__main__":
    sample_list = [1, 2, 3, 4, 5]
    iterator = iter(sample_list)
    peekable = PeekableInterface(iterator)

    print(peekable.peek())
    print(peekable.hasNext())

    print(peekable.next())
    print(peekable.next())
    print(peekable.next())

    print(peekable.peek())
    print(peekable.hasNext())

    print(peekable.next())
    print(peekable.hasNext())
    print(peekable.peek())
    print(peekable.next())

    print(peekable.hasNext())
    print(peekable.peek())

    print()

    sample_list = []
    iterator = iter(sample_list)
    peekable = PeekableInterface(iterator)

    print(peekable.peek())
    print(peekable.hasNext())