Add ctypes support for python3's recipe

doc/source/buildoptions.rst

@@ -27,6 +27,10 @@ and works with any recent version of the Android NDK.
 Select Python 3 by adding it to your requirements,
 e.g. ``--requirements=python3``.
 
+.. note:: ctypes is not included automatically, if you would like to use it
+          then add libffi to your requirements,
+          e.g. ``--requirements=kivy,libffi,python3``.
+
 
 CrystaX python3
 ###############

pythonforandroid/bootstraps/sdl2/build/src/main/java/org/kivy/android/PythonUtil.java

@@ -37,6 +37,7 @@ protected static ArrayList<String> getLibraries(File filesDir) {
         ArrayList<String> libsList = new ArrayList<String>();
         addLibraryIfExists(libsList, "crystax", libsDir);
         addLibraryIfExists(libsList, "sqlite3", libsDir);
+        addLibraryIfExists(libsList, "ffi", libsDir);
         libsList.add("SDL2");
         libsList.add("SDL2_image");
         libsList.add("SDL2_mixer");

pythonforandroid/recipes/python3/__init__.py

@@ -1,4 +1,4 @@
-from pythonforandroid.recipe import TargetPythonRecipe
+from pythonforandroid.recipe import TargetPythonRecipe, Recipe
 from pythonforandroid.toolchain import shprint, current_directory
 from pythonforandroid.logger import logger, info, error
 from pythonforandroid.util import ensure_dir, walk_valid_filens
@@ -33,16 +33,38 @@
 
 
 class Python3Recipe(TargetPythonRecipe):
+    '''
+    .. note::
+        In order to build certain python modules, we need to add some extra
+        recipes to our build requirements:
+
+            - ctypes: you must add the recipe for ``libffi``.
+    '''
     version = '3.7.1'
     url = 'https://www.python.org/ftp/python/{version}/Python-{version}.tgz'
     name = 'python3'
 
     depends = ['hostpython3']
     conflicts = ['python3crystax', 'python2']
+    opt_depends = ['libffi']
 
     # This recipe can be built only against API 21+
     MIN_NDK_API = 21
 
+    def set_libs_flags(self, env, arch):
+        '''Takes care to properly link libraries with python depending on our
+        requirements and the attribute :attr:`opt_depends`.
+        '''
+        if 'libffi' in self.ctx.recipe_build_order:
+            info('Activating flags for libffi')
+            recipe = Recipe.get_recipe('libffi', self.ctx)
+            include = ' -I' + ' -I'.join(recipe.get_include_dirs(arch))
+            ldflag = ' -L' + join(recipe.get_build_dir(arch.arch),
+                                  recipe.get_host(arch), '.libs') + ' -lffi'
+            env['CPPFLAGS'] = env.get('CPPFLAGS', '') + include
+            env['LDFLAGS'] = env.get('LDFLAGS', '') + ldflag
+        return env
+
     def build_arch(self, arch):
         if self.ctx.ndk_api < self.MIN_NDK_API:
             error('Target ndk-api is {}, but the python3 recipe supports only {}+'.format(
@@ -119,6 +141,8 @@ def build_arch(self, arch):
 
             env['SYSROOT'] = sysroot
 
+            env = self.set_libs_flags(env, arch)
+
             if not exists('config.status'):
                 shprint(sh.Command(join(recipe_build_dir, 'configure')),
                         *(' '.join(('--host={android_host}',

testapps/setup_testapp_python3.py

@@ -2,7 +2,7 @@
 from distutils.core import setup
 from setuptools import find_packages
 
-options = {'apk': {'requirements': 'sdl2,pyjnius,kivy,python3',
+options = {'apk': {'requirements': 'libffi,sdl2,pyjnius,kivy,python3',
                    'android-api': 27,
                    'ndk-api': 21,
                    'dist-name': 'bdisttest_python3_googlendk',