restartable.py

class Restartable(object):
    def __init__(self, iterable):
        self._iterable = iterable
        self._cache = None

    def __iter__(self):
        if not self._cache:
            if iter(self._iterable) is iter(self._iterable):
                self._cache = list(self._iterable)
            else:
                self._cache = self._iterable
        return iter(self._cache)