scipy.optimize.fmin_l_bfgs_b 'float' object not callable

Question

I am experiencing 'float' object is not callable error when I use scipy.optimize.fmin_l_bfgs_b function.

As a variables of the function, I put

vec_final = op.fmin_l_bfgs_b(m.mod(b,n)[0],vec,m.mod(b,n)[1]).

m.mod is a subroutine mod of module m , which has output P and gradient of P. I used f2py to call this fortran subroutine to python.

(P = float, P gradient = array)

May I know what could be the problem? Thank you!!