关于Python二分法求值的一个问题！求哥哥们快来帮忙！小白比较弱。。。。。

Question

#下面的代码是二分法求信用卡每月最低还款的题，这是正确代码 def pay(balance,annualInterestRate):     if balance<=0:         return None     low=balance/12.0     high=(balance*(1+annualInterestRate/12.0)**12)/12.0     while True:         b=balance         pay2=(low+high)/2         for i in range(12):             b=(b-pay2)*(1+annualInterestRate/12.0)         if abs(b)<=0.01:             return pay2         elif b>0.01:             low=pay2         else:             high=pay2 print pay(320000,0.2) #这是错误代码！请问这下面应该怎么改，应该是错在while的代码块！求问用while写的话怎么改？？ def pay(balance,annualInterestRate):     if balance<=0:         return None     b=balance     low=b/12.0     high=(b*(1+annualInterestRate/12.0)**12)/12.0     pay2=(low+high)/2     while b>0.01:         if pay2>b*(1+annualInterestRate/12):             high=pay2         else:             low=pay2         pay2=(low+high)/2.0         b=(b-pay2)*(1+annualInterestRate/12.0)     return pay2 print pay(320000,0.2)还想弱弱的问一下？这个能不能通过牛顿拉夫逊算法计算？