def dist(a, b):
    return sum((i-j)**2 for i, j in zip(a, b))
def __init__(self, root, cwd, files, badfn=None):
        super(exactmatcher, self).__init__(root, cwd, badfn)

        if isinstance(files, list):
            self._files = files
        else:
            self._files = list(files)