%cython
from sage.libs.gmp.all cimport *

cpdef float simple(double a):
    cdef mpf_t x
    mpf_init(x)
    mpf_set_d(x,a)
    return mpf_get_f(x)



Error compiling Cython file:
------------------------------------------------------------
...
include "cdefs.pxi"
from sage.libs.gmp.all cimport *

cpdef float simple(double a):
    cdef mpf_t x
    mpf_init(x)
             ^
------------------------------------------------------------

_Users_pdehaye__sage_sage_notebook_sagenb_home_admin_2_code_sage237_spyx_0.pyx:10:14: Cannot convert 'mpf_t' to Python object