# Double precision complex in f2py

## f2py and `Complex*16`

double precision

You may run into a subtle yet critical problem using double precision complex numbers between Fortran and Python using f2py. The real issue is that f2py doesn’t seem to understand the kind parameters we specify when assigning a variable. So f2py assumes your complex numbers are single precision (8 bytes per complex number) instead of double precision (16 bytes per complex number).

You won’t get an error on compiling, but your Python program importing the Fortran .so module will give erroneous results.

## Solution

Assuming

- program has
`use, intrinsic :: iso_c_binding, only: sp=>C_FLOAT, dp=>C_DOUBLE`

- assign your double-precision complex variable like
`complex(dp) :: x`

- copy file
`.f2py_f2cmap`

into the top directory of your Python project (where`setup.py`

is), containing:`dict(real= dict(sp='float', dp='double'), complex = dict(sp='complex_float',dp="complex_double"))`

## Notes

At this time it appears we don’t use the `C_DOUBLE_COMPLEX`

from `iso_c_binding`

,
I notice that F90Wrap does the same.

** Tags: **
f2py