def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def gerrity_score(self):
        """
        Gerrity Score, which weights each cell in the contingency table by its observed relative frequency.
        :return:
        """
        k = self.table.shape[0]
        n = float(self.table.sum())
        p_o = self.table.sum(axis=0) / n
        p_sum = np.cumsum(p_o)[:-1]
        a = (1.0 - p_sum) / p_sum
        s = np.zeros(self.table.shape, dtype=float)
        for (i, j) in np.ndindex(*s.shape):
            if i == j:
                s[i, j] = 1.0 / (k - 1.0) * (np.sum(1.0 / a[0:j]) + np.sum(a[j:k - 1]))
            elif i < j:
                s[i, j] = 1.0 / (k - 1.0) * (np.sum(1.0 / a[0:i]) - (j - i) + np.sum(a[j:k - 1]))
            else:
                s[i, j] = s[j, i]
        return np.sum(self.table / float(self.table.sum()) * s)