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Fortran to Python interface generator with derived type support

Project description

f90wrap: Fortran to Python interface generator with derived type support

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f90wrap is a tool to automatically generate Python extension modules
which interface to Fortran code that makes use of derived types. It
builds on the capabilities of the popular
[f2py]( utility by generating a
simpler Fortran 90 interface to the original Fortran code which is then
suitable for wrapping with f2py, together with a higher-level Pythonic
wrapper that makes the existance of an additional layer transparent to
the final user.

Copyright (C) James Kermode 2011-2016. Released under the GNU General
Public License, version 2. Originally based on f90doc - automatic
documentation generator for Fortran 90. Copyright (C) 2004 Ian Rutt.

If you would like to license the source code under different terms,
please contact James Kermode <>


1. [Python]( \>= 2.7 or 3.x (both now supported!)
2. Recent version of [numpy]( which includes `f2py`
3. Fortran compiler - tested with `gfortran` 4.6+ and recent `ifort` 12+


Installation is as follows:

git clone
cd f90wrap
python install [--prefix PREFIX]

f90wrap can also be installed using `conda` via the conda-forge channel:

conda config --add channels conda-forge

Once the conda-forge channel has been enabled, f90wrap can be installed with:

conda install f90wrap

It is possible to list all of the versions of f90wrap available on your platform with:

conda search f90wrap --channel conda-forge

Examples and Testing

To test the installation, run `make test` from the `examples/`
directory. You may find the code in the various examples useful.

Case studies

f90wrap has been used to wrap the following large-scale scientific

- [QUIP]( - molecular dynamics code
- [CASTEP]( - electronic structure code

See this [IPython notebook]( from a recent seminar for more details.


To use `f90wrap` to wrap a set of Fortran 90 source files and produce
wrappers suitable for input to f2py use:

f90wrap -m MODULE F90_FILES

where `MODULE` is the name of the Python module you want to produce (e.g.
the name of the Fortran code you are wrapping) and `F90_FILES` is a list
of Fortran 90 source files containing the modules, types and subroutines
you would like to expose via Python.

This will produce two types of output: Fortran 90 wrapper files suitable
for input to `f2py` to produce a low-level Python extension module, and a
high-level Python module desinged to be used together with the
f2py-generated module to give a more Pythonic interface.

One Fortran 90 wrapper file is written for each source file, named
`f90wrap_F90_FILE.f90`, plus possibly an extra file named
`f90wrap_toplevel.f90` if there are any subroutines or functions defined
outside of modules in `F90_FILES`.

To use f2py to compile these wrappers into an extension module, use:

f2py -c -m _MODULE OBJ_FILES f90wrap_*.f90 *.o

where `_MODULE` is the name of the low-level extension module.

Optionally, you can replace `f2py` with `f2py-f90wrap`, which is a
slightly modified version of `f2py` included in this distribution
that introduces the following features:

1. Allow the Fortran `present()` intrinsic function to work correctly with
optional arguments. If an argument to an f2py wrapped function is
optional and is not given, replace it with `NULL`.
2. Allow Fortran routines to raise a RuntimeError exception with a
message by calling an external function `f90wrap_abort`().
This is implemented using a `setjmp()/longjmp()` trap.
3. Allow Fortran routines to be interrupted with `Ctrl+C` by installing
a custom interrupt handler before the call into Fortran is made.
After the Fortran routine returns, the previous interrupt handler
is restored.


- Unlike standard `f2py`, `f90wrap` converts all `intent(out)` arrays to
`intent(in, out)`. This was a deliberate design decision to allow allocatable and automatic arrays of unknown output size to be used. It is hard in general to work out what size array needs to be allocated, so relying on the the user to pre-allocate from Python is the safest solution.
- Scalar arguments without `intent` are treated as `intent(in)` by `f2py`. To have `inout` scalars, you need to call `f90wrap` with the `--default-to-inout` flag and declare the python variables as 1-length numpy arrays (`numpy.zeros(1)` for example).
- Pointer arguments are not supported.
- Arrays of derived types are currently not fully supported: a workaround is provided for 1D-fixed-length arrays, i.e. `type(a), dimension(b) :: c`. In this case, the super-type `Type_a_Xb_Array` will be created, and the array of types can be accessed through `c.items`. Note that dimension b can not be `:`, but can be a parameter.

How f90wrap works

There are five steps in the process of wrapping a Fortran 90 routine to
allow it to be called from Python.

1. The Fortran source files are scanned, building up an
abstract symbol tree (AST) which describes all the modules, types,
subroutines and functions found.
2. The AST is transformed to remove nodes which
should not be wrapped (e.g. private symbols in modules, routines
with arguments of a derived type not defined in the project, etc.)
3. The `f90wrap.f90wrapgen.F90WrapperGenerator` class is used to write
a simplified Fortran 90 prototype for each routine, with derived
type arguments replaced by integer arrays containing a
representation of a pointer to the derived type, in the manner
described in
This allows opaque references to the
true Fortran derived type data structures to be passed back and
forth between Python and Fortran.
4. f2py is used to combine the F90 wrappers and the original compiled
functions into a Python extension module (optionally, f2py can be
replaced by f2py-f90wrap, a slightly modified version which adds
support for exception handling and interruption during exceution of
Fortran code).
5. The `f90wrap.pywrapgen.PythonWrapperGenerator` class is used to
write a thin object-oriented layer on top of the f2py generated
wrapper functions which handles conversion between Python object
instances and Fortran derived-type variables, converting arguments
back and forth automatically.

Advanced Features

Additional command line arguments can be passed to f90wrap to customize
how the wrappers are generated. See the `examples/` directory to see how
some of the options are used:

-h, --help show this help message and exit
-v, --verbose set verbosity level [default: None]
-V, --version show program's version number and exit
-p PREFIX, --prefix PREFIX
Prefix to prepend to arguments and subroutines.
-c [CALLBACK [CALLBACK ...]], --callback [CALLBACK [CALLBACK ...]]
Names of permitted callback routines.
Names of constructor routines.
Names of destructor routines.
-k KIND_MAP, --kind-map KIND_MAP
File containing Python dictionary in f2py_f2cmap
"File containing Python dictionary mapping string
length names to values
Default length of character strings
-i INIT_LINES, --init-lines INIT_LINES
File containing Python dictionary mapping type names
to necessary initialisation code
-I INIT_FILE, --init-file INIT_FILE
Python source file containing code to be added to
File containing Python dictionary to rename Fortran
--short-names SHORT_NAMES
File containing Python dictionary mapping full type
names to abbreviations
-m MOD_NAME, --mod-name MOD_NAME
Name of output extension module (without .so
-M, --move-methods Convert routines with derived type instance as first
agument into class methods
-P, --package Generate a Python package instead of a single module
-a ABORT_FUNC, --abort-func ABORT_FUNC
Name of Fortran subroutine to invoke if a fatal error
--only [ONLY [ONLY ...]]
Subroutines to include in wrapper
--skip [SKIP [SKIP ...]]
Subroutines to exclude from wrapper


James Kermode: <>


- Steven Murray [steven-murray](
- Greg Corbett [gregcorbett](
- Bob Fischer [citibob](
- David Verelst [davidovitch](
- James Orr [jamesorr](
- [yvesch](

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