Evaluate Newton’s polynomial using Python

''' p = evalPoly(a,xData,x).
    Evaluates Newton's polynomial p at x. The coefficient
    vector 'a' can be computed by the function 'coeffts'.
    a = coeffts(xData,yData).
    Computes the coefficients of Newton's polynomial.
def evalPoly(a,xData,x):
    n = len(xData) - 1  # Degree of polynomial
    p = a[n]
    for k in range(1,n+1):
        p = a[n-k] + (x -xData[n-k])*p
    return p
def coeffts(xData,yData):
    m = len(xData)  # Number of data points
    a = yData.copy()
    for k in range(1,m):
        a[k:m] = (a[k:m] - a[k-1])/(xData[k:m] - xData[k-1])
    return a

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