1. Packaging schema
Actors will be packaged using pip based approach. This way it will be possible to:
- install actors centrally
- install actors inside virtual environment
- host private PIP based repository
This section describes how packaging of an actor will look like and what will be the final structure of distributable package.
2. Sample code
Sample code (below) illustrates the way of embedding Fortran code inside Python. We start with very simple Fortran routine (distance). As we intent to wrap the code inside Python, we have to provide iso_c_binding based code as well (this code will be called from Python). In final solution this code will be autogenerated.
module distance_module
use iso_c_binding
contains
subroutine distance_wrapper(v, t, d) bind(c, name="distance_wrapper")
real (c_float), intent(inout) :: v
real (c_float), intent(inout) :: t
real (c_float), intent(inout) :: d
call distance(v, t, d)
end subroutine
subroutine distance(v, t, d)
implicit none
real, intent(in) :: v
real, intent(out) :: t
real, intent(out) :: d
d = v * t
end subroutine
end module distance_module
What we eventually want to do is to be able to call something like this inside Python
from distance_wrapper.actor import distance
print('Distance: ', distance( 20.0, 2.0 ))
Even though in a sample project all the codes are part of the repo, in final solution most of the elements will be autogenerated. The only code (provided by user) will be Fortran one.
Sample application with two codes based scenario can be found here: https://github.com/mkopsnc/marmot
In order to run samples, simply follow instructions inside README.md file
3. Sample structure
Sample code has following structure
distance - for the convenience all the code is in one dir
|-- distance_c_wrapper - C based wrapper - layer that allows to call
| |-- Makefile Fortran code from Python
| |-- include
| | `-- distance_c_wrapper.h Note! All the code inside distance_c_wrapper
| `-- src will be autogenerated. Shape of the code will depend
| |-- distancewrapper on project definition (description of what is supposed
| | `-- distance_c_wrapper.c to be generated)
| `-- main.c
|-- distance_fortran - This is the only code that will be provided by user
| |-- Makefile Result of the compilation is a lib##.a file that
| `-- src is later on packed inside shared lib that is called
| |-- distance from Python
| | `-- distance.F90
| `-- main.F90
`-- distance_python - Python based wrapper. This is the code that will
|-- MANIFEST.in be incorporated inside Python scripts/Python workflows
|-- README.md
|-- distance_wrapper
| |-- __init__.py Note! This code will be autogenerated (see above)
| `-- actor.py
|-- setup.cfg
`-- setup.py
4. Benefits of this approach
This approach allows to use the code in numerous scenarios
4.1. PYTHONPATH
It is possible to use the code directly inside script by simply exporting location of the code using PYTHONPATH.
> export PYTHONPATH=`pwd`/distance_python:${PYTHONPATH}
4.2. PIP install
Current structure allows to install wrapper inside central installation of Python or inside virtual environment. All we have to do is to use pip install.
> pip3 install --upgrade --force-reinstall `pwd`/distance_python
4.3. PIP repository
With this structure it is possible to generate compressed versions of pip packages and distribute them via custom, self hosted, pip repository.
5. References
- pip documentation: https://pip.pypa.io/en/stable/
- Packaging Python Projects: https://packaging.python.org/tutorials/packaging-projects/
- Packaging Python Projects - Hosting your own simple repository: https://packaging.python.org/guides/hosting-your-own-index/
- ISO_C_BINDING: https://gcc.gnu.org/onlinedocs/gfortran/ISO_005fC_005fBINDING.html