def degrees_of_freedom(self):
if len(self._set_xdata)==<NUM_LIT:0> or len(self._set_ydata)==<NUM_LIT:0>: return None<EOL>r = self.studentized_residuals()<EOL>if r == None: return<EOL>N = <NUM_LIT:0.0><EOL>for i in range(len(r)): N += len(r[i])<EOL>return N-len(self._pnames)<EOL>
Returns the number of degrees of freedom.