docs: def build(target_python, requirements):
      """
      Builds an APK given a target Python and a set of requirements.
      """
      if not requirements:
          return
      testapp = 'setup_testapp_python2.py'
      android_sdk_home = os.environ['ANDROID_SDK_HOME']
      android_ndk_home = os.environ['ANDROID_NDK_HOME']
      if target_python == TargetPython.python3:
          testapp = 'setup_testapp_python3_sqlite_openssl.py'
      requirements.add(target_python.name)
      requirements = ','.join(requirements)
      logger.info('requirements: {}'.format(requirements))
      with current_directory('testapps/'):
          # iterates to stream the output
          for line in sh.python(
                  testapp, 'apk', '--sdk-dir', android_sdk_home,
                  '--ndk-dir', android_ndk_home, '--bootstrap', 'sdl2', '--requirements',
                  requirements, _err_to_out=True, _iter=True):
              print(line)