def _fill_diagonals(self, m):
assert m.shape == (self.nsites, N_CODON, N_CODON)<EOL>for r in range(self.nsites):<EOL><INDENT>scipy.fill_diagonal(m[r], <NUM_LIT:0>)<EOL>m[r][self._diag_indices] -= scipy.sum(m[r], axis=<NUM_LIT:1>)<EOL><DEDENT>
Fills diagonals of `nsites` matrices in `m` so rows sum to 0.