```
import sys
from PyQt5.QtWidgets import QApplication, QWidget
from PyQt5.QtCore import QPointF ,QRectF ,Qt
from PyQt5.QtGui import QPainterPath ,QPainter ,QPen
from scipy import interpolate

class App(QWidget):

    def __init__(self):
        super().__init__()
        self.setWindowTitle('hogetta')
        self.setGeometry( 500, 50 , 500 , 500 )
        # self.setMouseTracking (True)  # <----------------*****
        # self.list=[[0,255] , [125, 125 ] , [255,0] ]   #  curve points  0,2:fix  1:variable
        self.x=[0,125,255]  # to use scipy function
        self.y=[255,125,0]
        self.f_list=[]      # look up table ( curve )
        for l in range(256):
            self.f_list.append(QPointF( l , l))   # make initial table --> line
        self.a = QPointF(4,4) # Tolerance in detecting point
        self.pselected = -1             # selectedpoint
        self.pmove = 0                  # move flag
        self.show()

    def mouseMoveEvent(self ,e):
        if self.pmove :  # Dorag ing
            # self.list[1] = e.pos()    # 1 only now
            self.x[1] = e.pos().x()
            self.y[1] = e.pos().y()
            self.makedata()
            self.update()

    def mousePressEvent(self ,e):
        self.pmove = True
    def mouseReleaseEvent(self ,e):
        self.pmove = False

    def makedata(): # make function , make table
        func = interpolate.interp1d(x, y, kind="cubic") # <------------
        for l in range(256):
            self.f_list[l] = QPointF( l , func(l) )

    def paintEvent (self,e):

        painter= QPainter()
        painter.begin(self) 
        for l in range( 256 )
            painter.drawPoint( self.f_list[l] )
        painter.end() 

if __name__ == "__main__":
    app = QApplication(sys.argv)
    ex = App()
    sys.exit(app.exec_())
```