utils.py

            # find QGIS Path
            if sys.platform == 'darwin':
                # search for the QGIS.app
                import qgis, re
                assert '.app' in qgis.__file__, 'Can not locate path of QGIS.app'
                PATH_QGIS_APP = re.split(r'\.app[\/]', qgis.__file__)[0] + '.app'
                PATH_QGIS = os.path.join(PATH_QGIS_APP, *['Contents', 'MacOS'])

                if not 'GDAL_DATA' in os.environ.keys():
                    os.environ['GDAL_DATA'] = r'/Library/Frameworks/GDAL.framework/Versions/Current/Resources/gdal'

                QApplication.addLibraryPath(os.path.join(PATH_QGIS_APP, *['Contents', 'PlugIns']))
                QApplication.addLibraryPath(os.path.join(PATH_QGIS_APP, *['Contents', 'PlugIns', 'qgis']))


            else:
                # assume OSGeo4W startup
                PATH_QGIS = os.environ['QGIS_PREFIX_PATH']

        assert os.path.exists(PATH_QGIS)

        qgsApp = QgsApplication([], True)
        qgsApp.setPrefixPath(PATH_QGIS, True)
        qgsApp.initQgis()

        def printQgisLog(tb, error, level):
            if error not in ['Python warning']:
                print(tb)

        QgsApplication.instance().messageLog().messageReceived.connect(printQgisLog)

        return qgsApp


def createCRSTransform(src, dst):
    assert isinstance(src, QgsCoordinateReferenceSystem)
    assert isinstance(dst, QgsCoordinateReferenceSystem)
    t = QgsCoordinateTransform()
    t.setSourceCrs(src)
    t.setDestinationCrs(dst)
    return t

if __name__ == '__main__':
    #nice predecessors

    qgsApp = initQgisApplication()
    se = SpatialExtent.world()
    assert nicePredecessor(26) == 25
    assert nicePredecessor(25) == 25
    assert nicePredecessor(23) == 20
    assert nicePredecessor(999) == 950
    assert nicePredecessor(1001) == 1000
    assert nicePredecessor(1.2) == 1.0      #
    assert nicePredecessor(0.8) == 0.5
    assert nicePredecessor(0.2) == 0.1
    assert nicePredecessor(0.021) == 0.01
    assert nicePredecessor(0.0009991) == 0.0005