python实现求平方根精确到0.01

def sqrt(a):
    if a < 0:
        return -1

    i, j = 0, a
    while i<= j:
        mid = (i+j)/2
        if abs(mid**2-a)<=0.01:
            return mid
        elif mid**2-a>0.01:
            j = mid
        else:
            i = mid