Proper way to reset csv.reader for multiple iterations?

Having an issue with a custom iterator in that it will only iterate over the file once. I am calling seek(0) on the relevant file object in between iterations, but StopIteration is thrown on the first call to next() on the 2nd run through. I feel I am overlooking something obvious, but would appreciate some fresh eyes on this:

class MappedIterator(object):
    """
    Given an iterator of dicts or objects and a attribute mapping dict, 
    will make the objects accessible via the desired interface.

    Currently it will only produce dictionaries with string values. Can be 
    made to support actual objects later on. Somehow... :D
    """

    def __init__(self, obj=None, mapping={}, *args, **kwargs):

        self._obj = obj
        self._mapping = mapping
        self.cnt = 0

    def __iter__(self):

        return self

    def reset(self):

        self.cnt = 0

    def next(self):

        try:

            try:
                item = self._obj.next()
            except AttributeError:
                item = self._obj[self.cnt]

            # If no mapping is provided, an empty object will be returned.
            mapped_obj = {}

            for mapped_attr in self._mapping:

                attr = mapped_attr.attribute
                new_attr = mapped_attr.mapped_name

                val = item.get(attr, '')
                val = str(val).strip() # get rid of whitespace

                # TODO: apply transformers...

                # This allows multi attribute mapping or grouping of multiple
                # attributes in to one.
                try:
                    mapped_obj[new_attr] += val
                except KeyError:
                    mapped_obj[new_attr] = val

            self.cnt += 1

            return mapped_obj

        except (IndexError, StopIteration):

            self.reset()
            raise StopIteration


class CSVMapper(MappedIterator):

    def __init__(self, rea