Final temprerature error (standard deviation)

Teff = [6240, 6257, 6038]
TeffSum = 0
Er = 0
Error = 0
for f in range(0,3):
    TeffSum += Teff[f]
    print("TeffSum", TeffSum)
TeffAver = float(TeffSum/(f+1))
print("TeffAver", TeffAver)
for f in range(0,3): 
    Er = (Teff[f]-TeffAver)**2 
    Error = Error + Er
    print("Error", Error)
ErrorAverage = Error / (f+1)
print("ErrorAverage", ErrorAverage)
TeffError = math.sqrt(ErrorAverage)/(f+2)
print("TeffError", TeffError)