Scratch

def timesLst(num, lst):
    a1 = lst
    return ([x*num for x in a1])

def subLsts(L1,L2):
    '''returns L1 - L2'''
    ans = []
    for i in range (0, len(L1)):
        ans += [L1[i]-L2[i]]
    return (ans)

def zeroRow(clmn, EQs):
    '''This function is ment to add a row of 0's to a system of '''\
            '''equations, given a list [[coef1, coef2, coef3...value].[coef1...]]'''
    newEQs = []
    for i in range(0, len(EQs)):
        multNum = 1
        for j in range (0,i):
            multNum *= EQs[j][clmn]
        for j in range ((i+1), len(EQs)):
            multNum *= EQs[j][clmn]
        newEQs += [timesLst(multNum, EQs[i])]
    EQs = newEQs
    newEQs = [EQs[0]]
    for i in range (1, len(EQs)):
        newEQs += [subLsts(EQs[0],EQs[i])]
    return (newEQs)

def ref(EQs):
    copyEQs = EQs
    finalMatrix = [EQs[0]]
    finalAns = []
    for EQ in EQs:
        if len(EQ) != (len(EQs)+1):
            return ("Error")
    else:
        for clmn in range (0, len(EQs[0])-2):
            EQs = zeroRow(clmn, EQs)[1:]
            finalMatrix += [EQs[0]]
        rowEchelon = []
        for i in range(0, len(copyEQs)):
            rowEchelon += [timesLst((1/(finalMatrix[i][i])), finalMatrix[i])]
        return (rowEchelon)

def makeString(coefs):
    ans = "y = "
    for i in range(0,len(coefs)):
        x = str(coefs[-i-1])+"*x^"+str(len(coefs)-i-1)+" + "
        ans += x
    return (ans[:-3])   

def findPoly(points):
    for point in points:
        if points.count(point) != 1 or len(point) != 2:
            return (False)
    degree = len(points)-1
    matrix = []
    for i in range(0, len(points)):
        matrix += [[]]
        for j in range (0, degree+1):
            matrix[i] += [(points[i][0])**(degree-j)]
        matrix[i] += [points[i][1]]
    matrix = ref(matrix)
    h = len(matrix)
    l = len(matrix[0])
    seed = (matrix[-1][-1]/matrix[-1][-2])
    coef = [seed]
    for i in range(0, h-1):
        amt = 0
        value = matrix[-i-2][-1]
        for j in range(0,l-2):
            amt += (matrix[-i-2][-j-2])*coef[j]
    coef += [value - amt]
    return (makeString(coef))

Traceback (most recent call last):
  File "<pyshell#218>", line 1, in <module>
    findPoly([(-2,2),(2,-4),(1,-2.5)])
  File "C:\Python32\solveSystem.py", line 73, in findPoly
    amt += (matrix[-i-2][-j-2])*coef[j]
IndexError: list index out of range