Passing numpy string-format arrays to fortran using f2py

Question

My aim is to print the 2nd string from a python numpy array in fortran, but I only ever get the first character printed, and it's not necessarily the right string either.

Can anyone tell me what the correct way to pass full string arrays to fortran?

The code is as follows:

testpy.py

import numpy as np
import testa4

strvar = np.asarray(['aa','bb','cc'], dtype = np.dtype('a2'))
testa4.testa4(strvar)

testa4.f90

subroutine testa4(strvar)
implicit none

character(len=2), intent(in) :: strvar(3)
!character*2 does not work here - why?

print *, strvar(2)

end subroutine testa4

Compiled with

f2py -c -m testa4 testa4.f90

Output of above code

c

Desired output

bb

Answer 1

I don't know how to do that using f2py. But it can be done with ctypes. You get an array of characters, but you can convert it to a string very easily.

subroutine testa4(strvar) bind(C, name='testa4')
  use iso_c_binding
  implicit none

  character(len=1,kind=c_char), intent(in) :: strvar(2,3)

  print *, strvar(:,2)

end subroutine testa4

compile: gfortran -shared -fPIC testa4.f90 -o testa4.so

import numpy as np
import ctypes

testa4 = ctypes.CDLL("./testa4.so")

strvar = np.asarray(['aa','bb','cc'], dtype = np.dtype('a2'))
strvar_p = ctypes.c_void_p(strvar.ctypes.data)

testa4.testa4(strvar_p)

run:

> python testpy.f90 
 bb