为什么我得到 NameError: name 'self' is not defined？

Question

当我尝试运行此 python 代码时：def convertProjection(self,x,y,from_crs,to_crs):    crsSrc = QgsCoordinateReferenceSystem(from_crs)    crsDest = QgsCoordinateReferenceSystem(to_crs)    xform = QgsCoordinateTransform(crsSrc, crsDest)    pt = xform.transform(QgsPoint(x,y))    return pt.x, pt.y# Remove the "EPSG:" partfrom_crs = 3857to_crs = 4326x = -11705274.6374y = 4826473.6922lon, lat = self.convertProjection(x,y,from_crs,to_crs)发生此错误：/usr/bin/python3.5 /home/jithin/PycharmProjects/PythonTests/XYTOLatLong_Conversion.pyTraceback (most recent call last):  File "/home/jithin/PycharmProjects/PythonTests/XYTOLatLong_Conversion.py", line 36, in <module>    lon, lat = self.convertProjection(x,y,from_crs,to_crs)NameError: name 'self' is not defined任何帮助表示赞赏......谢谢......