f2py-with-derived-types

f2py is a tool which provides a connection between the Fortran and Python languages. It is overall and excellent tool. However, it can not easily generate a Python interface for Fortran derived types.

This repository shows that, with some effort, you can wrap a fortran derived type.

myobjects.f90 contains a derived type mytype:

type mytype
  real(real_kind), allocatable :: arr(:)
contains
  procedure :: sumarr
  procedure :: printarr
end type

mytype has an allocatable array, named arr, and two type-bound procedures that do things to arr. The goal here is to make a python interface to mytype

The files mytype_wrapper.f90 and MyType.py provide this wrapper to mytype. They key to this approach is keeping track of an instance of mytype with a pointer. This pointer is passed between wrapper functions. Take a close look at mytype_wrapper.f90 and MyType.py to understand.

To compile, run

gfortran -c myobjects.f90
f2py -c myobjects.o mytype_wrapper.f90 -m _mytype_wrapper

Then you can use the wrapper with code like

from MyType import MyType
my = MyType()
my.arr = [1,2,3]
print(my.summarr())