使用二分法（Bisection Method）求平方根。

def sqrtBI(x, epsilon):

assert x>0, 'X must be non-nagtive, not ' + str(x)

assert epsilon > 0, 'epsilon must be postive, not ' + str(epsilon)

low = 0

high = x

guess = (low + high)/2.0

counter = 1

while (abs(guess ** 2 - x) > epsilon) and (counter <= 100):

if guess ** 2 < x:

low = guess

else :

high = guess

guess = (low + high)/2.0

counter += 1

return guess

验证一下。

上面的方法，如果 X