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========================
Advanced F2PY use cases
========================
Adding user-defined functions to F2PY generated modules
=========================================================
User-defined Python C/API functions can be defined inside
signature files using ``usercode`` and ``pymethoddef`` statements
(they must be used inside the ``python module`` block). For
example, the following signature file ``spam.pyf``
.. include:: ./code/spam.pyf
:literal:
wraps the C library function ``system()``::
f2py -c spam.pyf
In Python this can then be used as:
.. literalinclude:: ./code/results/spam_session.dat
:language: python
Adding user-defined variables
==============================
The following example illustrates how to add user-defined variables to a F2PY
generated extension module by modifying the dictionary of a F2PY generated
module. Consider the following signature file (compiled with ``f2py -c var.pyf``):
.. literalinclude:: ./code/var.pyf
:language: fortran
Notice that the second ``usercode`` statement must be defined inside
an ``interface`` block and the module dictionary is available through
the variable ``d`` (see ``varmodule.c`` generated by ``f2py var.pyf`` for
additional details).
Usage in Python:
.. literalinclude:: ./code/results/var_session.dat
:language: python
Dealing with KIND specifiers
============================
Currently, F2PY can handle only ``<type spec>(kind=<kindselector>)``
declarations where ``<kindselector>`` is a numeric integer (e.g. 1, 2,
4,...), but not a function call ``KIND(..)`` or any other
expression. F2PY needs to know what would be the corresponding C type
and a general solution for that would be too complicated to implement.
However, F2PY provides a hook to overcome this difficulty, namely,
users can define their own <Fortran type> to <C type> maps. For
example, if Fortran 90 code contains::
REAL(kind=KIND(0.0D0)) ...
then create a mapping file containing a Python dictionary::
{'real': {'KIND(0.0D0)': 'double'}}
for instance.
Use the ``--f2cmap`` command-line option to pass the file name to F2PY.
By default, F2PY assumes file name is ``.f2py_f2cmap`` in the current
working directory.
More generally, the f2cmap file must contain a dictionary
with items::
<Fortran typespec> : {<selector_expr>:<C type>}
that defines mapping between Fortran type::
<Fortran typespec>([kind=]<selector_expr>)
and the corresponding <C type>. The <C type> can be one of the following::
char
signed_char
short
int
long_long
float
double
long_double
complex_float
complex_double
complex_long_double
string
For more information, see the F2Py source code ``numpy/f2py/capi_maps.py``.
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