Call Cython via python -m Cython rather than system-wide binary

- call Cython via `python -m Cython` to avoid picking one not matching
  the current python version (which can happen if just calling `Cython`)
- this should fix #1885

pythonforandroid/build.py

@@ -27,14 +27,6 @@
     RECOMMENDED_NDK_API, RECOMMENDED_TARGET_API)
 
 
-def get_cython_path():
-    for cython_fn in ("cython", "cython3", "cython2", "cython-2.7"):
-        cython = sh.which(cython_fn)
-        if cython:
-            return cython
-    raise BuildInterruptingException('No cython binary found.')
-
-
 def get_ndk_platform_dir(ndk_dir, ndk_api, arch):
     ndk_platform_dir_exists = True
     platform_dir = arch.platform_dir
@@ -111,7 +103,6 @@ class Context(object):
     use_setup_py = False
 
     ccache = None  # whether to use ccache
-    cython = None  # the cython interpreter name
 
     ndk_platform = None  # the ndk platform directory
 
@@ -374,7 +365,6 @@ def prepare_build_environment(self,
         if not self.ccache:
             info('ccache is missing, the build will not be optimized in the '
                  'future.')
-        self.cython = get_cython_path()
 
         # This would need to be changed if supporting multiarch APKs
         arch = self.archs[0]

pythonforandroid/recipe.py

@@ -1024,8 +1024,12 @@ def cythonize_file(self, env, build_dir, filename):
             del cyenv['PYTHONPATH']
         if 'PYTHONNOUSERSITE' in cyenv:
             cyenv.pop('PYTHONNOUSERSITE')
-        cython_command = sh.Command(self.ctx.cython)
-        shprint(cython_command, filename, *self.cython_args, _env=cyenv)
+        cython_command = sh.Command(
+            "python" +
+            self.ctx.python_recipe.major_minor_version_string.split(".")[0]
+        )
+        shprint(cython_command, "-m", "Cython",
+                filename, *self.cython_args, _env=cyenv)
 
     def cythonize_build(self, env, build_dir="."):
         if not self.cythonize:

tests/test_toolchain.py

@@ -68,8 +68,6 @@ def test_create(self):
         ) as m_get_toolchain_versions, mock.patch(
             'pythonforandroid.build.get_ndk_platform_dir'
         ) as m_get_ndk_platform_dir, mock.patch(
-            'pythonforandroid.build.get_cython_path'
-        ) as m_get_cython_path, mock.patch(
             'pythonforandroid.toolchain.build_recipes'
         ) as m_build_recipes, mock.patch(
             'pythonforandroid.bootstraps.service_only.'
@@ -84,7 +82,6 @@ def test_create(self):
             mock.call('/tmp/android-sdk')]
         assert m_get_toolchain_versions.call_args_list == [
             mock.call('/tmp/android-ndk', mock.ANY)]
-        assert m_get_cython_path.call_args_list == [mock.call()]
         build_order = [
             'hostpython3', 'libffi', 'openssl', 'sqlite3', 'python3',
             'genericndkbuild', 'setuptools', 'six', 'pyjnius', 'android',