用python二分法求平方根,这个程序为什么错了?

首先二分法肯定需要一个“不断”二分的过程,你的代码里面连一个循环都没有,肯定是不对的吧?
其次按照你的代码的思路,如果当前估算值guess的平法比x大,那就往0那边靠,否则就往1那边靠,这个好像也不对吧?
二分法的实现方法应该是,在区间[left,right]里面找x的开方,令估算值为guess等于区间的中点,如果guess比实际的大,那就把区间缩小一半,令到右端点移动到中点,如果guess比实际的小,也是将区间缩小一半,但是是令左端点移动到中点.这样每次缩小一半的区间,直到区间的长度非常非常小,那就认为区间的两个端点是相等的了,这个时候就得到了答案.
import math

def main():
x09x = input('x=')
x09n = 0
x09if x <= 1 and x >= 0:
x09x09left = 0.
x09x09right = 1.
x09x09while right - left >= 0.0000001:
x09x09x09guess = (left + right) / 2.
x09x09x09if guess ** 2 - x >= 0.0000001:
x09x09x09x09right = guess
x09x09x09else:
x09x09x09x09left = guess
x09x09#return guess
x09x09print 'sqrt(x) is', left
x09else:
x09x09print 'x should be in [0,1]'

if __name__ == '__main__':
x09main()
我按照你的思路又写了另外一种方法：
def second():
x09x = input('x=')
x09n = 0
x09if x <= 1 and x >= 0:
x09x09movelen = (1 + 0) / 4.
x09x09guess = (1 + 0) / 2.
x09x09while abs(guess ** 2 - x) >= 0.0000001:
x09x09x09if (guess ** 2 - x) >= 0.0000001:
x09x09x09x09guess = guess - movelen
x09x09x09else:
x09x09x09x09guess = guess + movelen
x09x09x09movelen = movelen / 2.
x09x09print 'sqrt(x) is', guess
x09else:
x09x09print 'x should be in [0,1]'