Python help

What would be suitable where the missing code goes? The #? spot

import numpy as np

from scipy.optimize import curve_fit

import matplotlib.pyplot as pyplot

from math import floor, ceil

def RSquared(x,y,coeff):

AvgY=np.mean(y) #calculates the average value of y

SSTot=0

SSRes=0

ymodel=Poly(x,*coeff)

for i in range(len(y)):

SSTot+=(y[i]-AvgY)**2

SSRes+=(y[i]-ymodel[i])**2

RSq= ?

return RSq

def Poly(xdata, *a):

y = np.zeros_like(xdata)

power = len(a)-1

for i in range(power+1):

for j in range(len(xdata)):

x=xdata[j]

c=a[i]

y[j] += c*x**i

return y

def PlotLeastSquares(x, y, coeff, showpoints=True, npoints=500):