How to produce swig interface files#

This section describes how Modula-2 implementation modules can be called from Python (and other scripting languages such as TCL and Perl). GNU Modula-2 can be instructed to create a swig interface when it is compiling an implementation module. Swig then uses the interface file to generate all the necessary wrapping to that the desired scripting language may access the implementation module.

Here is an example of how you might call upon the services of the Modula-2 library module NumberIO from Python3.

The following commands can be used to generate the Python3 module:

export src=directory to the sources
export prefix=directory to where the compiler is installed
gm2 -I${src} -c -g -fswig ${src}/../../../gm2-libs/NumberIO.mod
gm2 -I${src} -c -g -fmakelist ${src}/../../../gm2-libs/NumberIO.mod

gm2 -I${src} -c -g -fmakeinit -fshared \
   ${src}/../../../gm2-libs/NumberIO.mod

swig -c++ -python3 NumberIO.i

libtool --mode=compile g++ -g -c -I${src} NumberIO_m2.cpp \
  -o NumberIO_m2.lo

libtool --tag=CC --mode=compile gm2 -g -c \
  -I${src}../../../gm2-libs \
  ${src}/../../../gm2-libs/NumberIO.mod -o NumberIO.lo

libtool --tag=CC --mode=compile g++ -g -c NumberIO_wrap.cxx \
  -I/usr/include/python3 -o NumberIO_wrap.lo

libtool --mode=link gcc -g NumberIO_m2.lo NumberIO_wrap.lo \
   -L${prefix}/lib64 \
   -rpath `pwd` -lgm2 -lstdc++ -lm -o libNumberIO.la

cp .libs/libNumberIO.so _NumberIO.so

The first four commands, generate the swig interface file NumberIO.i and python wrap files NumberIO_wrap.cxx and NumberIO.py. The next three libtool commnads compile the C++ and Modula-2 source code into .lo objects. The last libtool command links all the .lo files into a .la file and includes all shared library dependencies.

Now it is possible to run the following Python script (called testnum.py):

import NumberIO

print ("1234 x 2 =", NumberIO.NumberIO_StrToInt("1234")*2)

like this:

$ python3 testnum.py
1234 x 2 = 2468

See How to produce a Python module for another example which uses the UNQUALIFIED keyword to reduce the module name clutter from the viewport of Python3.