# Using F2PY

This page contains a reference to all command-line options for the `f2py` command, as well as a reference to internal functions of the `numpy.f2py` module.

## Using `f2py` as a command-line tool

When used as a command-line tool, `f2py` has three major modes, distinguished by the usage of `-c` and `-h` switches.

### 1. Signature file generation

To scan Fortran sources and generate a signature file, use

    f2py -h <filename.pyf> <options> <fortran files>   \
      [[ only: <fortran functions>  : ]                \
        [ skip: <fortran functions>  : ]]...           \
      [<fortran files> ...]

Note

A Fortran source file can contain many routines, and it is often not necessary to allow all routines to be usable from Python. In such cases, either specify which routines should be wrapped (in the `only: .. :` part) or which routines F2PY should ignore (in the `skip: .. :` part).

If `<filename.pyf>` is specified as `stdout`, then signatures are written to standard output instead of a file.

Among other options (see below), the following can be used in this mode:

> `--overwrite-signature`

>   Overwrites an existing signature file.

### 2. Extension module construction

To construct an extension module, use

    f2py -m <modulename> <options> <fortran files>   \
      [[ only: <fortran functions>  : ]              \
        [ skip: <fortran functions>  : ]]...          \
      [<fortran files> ...]

The constructed extension module is saved as `<modulename>module.c` to the current directory.

Here `<fortran files>` may also contain signature files. Among other options (see below), the following options can be used in this mode:

> `--debug-capi`

>   Adds debugging hooks to the extension module. When using this extension module, various diagnostic information about the wrapper is written to the standard output, for example, the values of variables, the steps taken, etc.

> `-include'<includefile>'`

>   Add a CPP `#include` statement to the extension module source. `<includefile>` should be given in one of the following forms

>       "filename.ext"
>       <filename.ext>

>   The include statement is inserted just before the wrapper functions. This feature enables using arbitrary C functions (defined in `<includefile>`) in F2PY generated wrappers.

>   Note

>   This option is deprecated. Use `usercode` statement to specify C code snippets directly in signature files.

> `--[no-]wrap-functions`

>   Create Fortran subroutine wrappers to Fortran functions. `--wrap-functions` is default because it ensures maximum portability and compiler independence.

> `--include-paths <path1>:<path2>:..`

>   Search include files from given directories.

> `--help-link [<list of resources names>]`

>   List system resources found by `numpy_distutils/system_info.py`. For example, try `f2py --help-link lapack_opt`.

### 3. Building a module

To build an extension module, use

    f2py -c <options> <fortran files>       \
      [[ only: <fortran functions>  : ]     \
        [ skip: <fortran functions>  : ]]... \
      [ <fortran/c source files> ] [ <.o, .a, .so files> ]

If `<fortran files>` contains a signature file, then the source for an extension module is constructed, all Fortran and C sources are compiled, and finally all object and library files are linked to the extension module `<modulename>.so` which is saved into the current directory.

If `<fortran files>` does not contain a signature file, then an extension module is constructed by scanning all Fortran source codes for routine signatures, before proceeding to build the extension module.

Among other options (see below) and options described for previous modes, the following options can be used in this mode:

> `--help-fcompiler`

>   List the available Fortran compilers.

> `--help-compiler` [depreciated]

>   List the available Fortran compilers.

> `--fcompiler=<Vendor>`

>   Specify a Fortran compiler type by vendor.

> `--f77exec=<path>`

>   Specify the path to a F77 compiler

> `--fcompiler-exec=<path>` [depreciated]

>   Specify the path to a F77 compiler

> `--f90exec=<path>`

>   Specify the path to a F90 compiler

> `--f90compiler-exec=<path>` [depreciated]

>   Specify the path to a F90 compiler

> `--f77flags=<string>`

>   Specify F77 compiler flags

> `--f90flags=<string>`

>   Specify F90 compiler flags

> `--opt=<string>`

>   Specify optimization flags

> `--arch=<string>`

>   Specify architecture specific optimization flags

> `--noopt`

>   Compile without optimization flags

> `--noarch`

>   Compile without arch-dependent optimization flags

> `--debug`

>   Compile with debugging information

> `-l<libname>`

>   Use the library `<libname>` when linking.

> `-D<macro>[=<defn=1>]`

>   Define macro `<macro>` as `<defn>`.

> `-U<macro>`

>   Define macro `<macro>`

> `-I<dir>`

>   Append directory `<dir>` to the list of directories searched for include files.

> `-L<dir>`

>   Add directory `<dir>` to the list of directories to be searched for `-l`.

> `link-<resource>`

>   Link the extension module with <resource> as defined by `numpy_distutils/system_info.py`. E.g. to link with optimized LAPACK libraries (vecLib on MacOSX, ATLAS elsewhere), use `--link-lapack_opt`. See also `--help-link` switch.

Note

The `f2py -c` option must be applied either to an existing `.pyf` file (plus the source/object/library files) or one must specify the `-m <modulename>` option (plus the sources/object/library files). Use one of the following options:

    f2py -c -m fib1 fib1.f

or

    f2py -m fib1 fib1.f -h fib1.pyf
    f2py -c fib1.pyf fib1.f

For more information, see the Building C and C++ Extensions Python documentation for details.

When building an extension module, a combination of the following macros may be required for non-gcc Fortran compilers:

    -DPREPEND_FORTRAN
    -DNO_APPEND_FORTRAN
    -DUPPERCASE_FORTRAN

To test the performance of F2PY generated interfaces, use `-DF2PY_REPORT_ATEXIT`. Then a report of various timings is printed out at the exit of Python. This feature may not work on all platforms, and currently only Linux is supported.

To see whether F2PY generated interface performs copies of array arguments, use `-DF2PY_REPORT_ON_ARRAY_COPY=<int>`. When the size of an array argument is larger than `<int>`, a message about the copying is sent to `stderr`.

### Other options

> `-m <modulename>`

>   Name of an extension module. Default is `untitled`.

> Warning

> Don’t use this option if a signature file (`*.pyf`) is used.

> `--[no-]lower`

>   Do [not] lower the cases in `<fortran files>`. By default, `--lower` is assumed with `-h` switch, and `--no-lower` without the `-h` switch.

> `-include<header>`

>   Writes additional headers in the C wrapper, can be passed multiple times, generates #include <header> each time. Note that this is meant to be passed in single quotes and without spaces, for example `'-include<stdbool.h>'`

> `--build-dir <dirname>`

>   All F2PY generated files are created in `<dirname>`. Default is `tempfile.mkdtemp()`.

> `--f2cmap <filename>`

>   Load Fortran-to-C `KIND` specifications from the given file.

> `--quiet`

>   Run quietly.

> `--verbose`

>   Run with extra verbosity.

> `--skip-empty-wrappers`

>   Do not generate wrapper files unless required by the inputs. This is a backwards compatibility flag to restore pre 1.22.4 behavior.

> `-v`

>   Print the F2PY version and exit.

Execute `f2py` without any options to get an up-to-date list of available options.

## Python module `numpy.f2py`

The f2py program is written in Python and can be run from inside your code to compile Fortran code at runtime, as follows:

    from numpy import f2py
    with open("add.f") as sourcefile:
        sourcecode = sourcefile.read()
    f2py.compile(sourcecode, modulename='add')
    import add

The source string can be any valid Fortran code. If you want to save the extension-module source code then a suitable file-name can be provided by the `source_fn` keyword to the compile function.

When using `numpy.f2py` as a module, the following functions can be invoked.

Warning

The current Python interface to the `f2py` module is not mature and may change in the future.

Fortran to Python Interface Generator.

numpy.f2py.compile(source, modulename='untitled', extra_args='', verbose=True, source_fn=None, extension='.f', full_output=False)

  Build extension module from a Fortran 77 source string with f2py.

  Parameters:
    source str or bytes

      Fortran source of module / subroutine to compile

      Changed in version 1.16.0: Accept str as well as bytes

    modulename str, optional

      The name of the compiled python module

    extra_args str or list, optional

      Additional parameters passed to f2py

      Changed in version 1.16.0: A list of args may also be provided.

    verbose bool, optional

      Print f2py output to screen

    source_fn str, optional

      Name of the file where the fortran source is written. The default is to use a temporary file with the extension provided by the `extension` parameter

    extension`{'.f', '.f90'}`, optional

      Filename extension if source_fn is not provided. The extension tells which fortran standard is used. The default is `.f`, which implies F77 standard.

      New in version 1.11.0.

    full_output bool, optional

      If True, return a `subprocess.CompletedProcess` containing the stdout and stderr of the compile process, instead of just the status code.

      New in version 1.20.0.

  Returns:
    result int or `subprocess.CompletedProcess`

      0 on success, or a `subprocess.CompletedProcess` if `full_output=True`

  Examples

      >>> import numpy.f2py
      >>> fsource = '''
      ...       subroutine foo
      ...       print*, "Hello world!"
      ...       end
      ... '''
      >>> numpy.f2py.compile(fsource, modulename='hello', verbose=0)
      0
      >>> import hello
      >>> hello.foo()
       Hello world!

numpy.f2py.get_include()

  Return the directory that contains the `fortranobject.c` and `.h` files.

  Note

  This function is not needed when building an extension with `numpy.distutils` directly from `.f` and/or `.pyf` files in one go.

  Python extension modules built with f2py-generated code need to use `fortranobject.c` as a source file, and include the `fortranobject.h` header. This function can be used to obtain the directory containing both of these files.

  Returns:
    include_path str

      Absolute path to the directory containing `fortranobject.c` and `fortranobject.h`.

  See also

  `numpy.get_include`

    function that returns the numpy include directory

  Notes

  New in version 1.21.1.

  Unless the build system you are using has specific support for f2py, building a Python extension using a `.pyf` signature file is a two-step process. For a module `mymod`:

  - Step 1: run `python -m numpy.f2py mymod.pyf --quiet`. This generates `_mymodmodule.c` and (if needed) `_fblas-f2pywrappers.f` files next to `mymod.pyf`.

  - Step 2: build your Python extension module. This requires the following source files:

    - `_mymodmodule.c`

    - `_mymod-f2pywrappers.f` (if it was generated in Step 1)

    - `fortranobject.c`

numpy.f2py.run_main(comline_list)

  Equivalent to running:

      f2py <args>

  where `<args>=string.join(<list>,' ')`, but in Python. Unless `-h` is used, this function returns a dictionary containing information on generated modules and their dependencies on source files.

  You cannot build extension modules with this function, that is, using `-c` is not allowed. Use the `compile` command instead.

  Examples

  The command `f2py -m scalar scalar.f` can be executed from Python as follows.

      >>> import numpy.f2py
      >>> r = numpy.f2py.run_main(['-m','scalar','doc/source/f2py/scalar.f'])
      Reading fortran codes...
              Reading file 'doc/source/f2py/scalar.f' (format:fix,strict)
      Post-processing...
              Block: scalar
                              Block: FOO
      Building modules...
              Building module "scalar"...
              Wrote C/API module "scalar" to file "./scalarmodule.c"
      >>> print(r)
      {'scalar': {'h': ['/home/users/pearu/src_cvs/f2py/src/fortranobject.h'],
      	 'csrc': ['./scalarmodule.c',
                        '/home/users/pearu/src_cvs/f2py/src/fortranobject.c']}}

## Automatic extension module generation

If you want to distribute your f2py extension module, then you only need to include the .pyf file and the Fortran code. The distutils extensions in NumPy allow you to define an extension module entirely in terms of this interface file. A valid `setup.py` file allowing distribution of the `add.f` module (as part of the package `f2py_examples` so that it would be loaded as `f2py_examples.add`) is:

    def configuration(parent_package='', top_path=None)
        from numpy.distutils.misc_util import Configuration
        config = Configuration('f2py_examples',parent_package, top_path)
        config.add_extension('add', sources=['add.pyf','add.f'])
        return config

    if __name__ == '__main__':
        from numpy.distutils.core import setup
        setup(**configuration(top_path='').todict())

Installation of the new package is easy using:

    pip install .

assuming you have the proper permissions to write to the main site- packages directory for the version of Python you are using. For the resulting package to work, you need to create a file named `__init__.py` (in the same directory as `add.pyf`). Notice the extension module is defined entirely in terms of the `add.pyf` and `add.f` files. The conversion of the .pyf file to a .c file is handled by `numpy.distutils`.