A peekable Python iterator

peekable.py

class Peekable:
    def __init__(self, it):
        self.it = it
        self.finished = False
        self.curr = None
        self.nextval = next(it)
    def __iter__(self):
        return self
    def __next__(self):
        if self.finished:
            raise StopIteratoin
        curr = self.nextval
        try:
            self.nextval = next(self.it)
        except StopIteration:
            self.finished = True
        return curr
    def peek(self):
        if self.finished:
            return None
        return self.nextval