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:" part

from_crs = 3857

to_crs = 4326

x = -11705274.6374

y = 4826473.6922

lon, lat = self.convertProjection(x,y,from_crs,to_crs)

发生此错误：

/usr/bin/python3.5 /home/jithin/PycharmProjects/PythonTests/XYTOLatLong_Conversion.py

Traceback (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......