无界整数类

Question

我正在实现一个叫做UnboundInteger的类，它的功能和普通整数一样。这个类的目的是能够处理任意大小的整数，也就是说，它的大小没有任何限制。

这是我的代码

class UnboundInteger(object):

def __init__(self, integer):
    self.integer = str(integer)


def __add__(self, other):
    carry = '0'
    temp = '0'
    result = ''

    if (len(self.integer) > len(other.integer)):
        num_of_zeros = len(self.integer) - len(other.integer)
        other.integer = '0' * num_of_zeros + other.integer

    elif (len(self.integer < other.integer)):
        num_of_zeros = len(other.integer) - len(self.integer)
        self.integer = '0' * num_of_zeros + self.integer

    for i in range(1, len(self.integer)+1):
        temp = str(int(self.integer[-i]) + int(other.integer[-i]) + int(carry))
        temp = '0' + temp
        temp = temp[-1]
        carry = temp[-2]
        result = temp + result

    return UnboundInteger(result)



@classmethod
def from_int(cls, integer):
    '''\
    Take in a integer and build the unbound integer object.
    '''
    ub_integer = cls(integer)
    return ub_integer

可惜我无法找到错误的原因，能帮我一下吗？

这是错误信息

    In [40]: reload(test)
Out[40]: <module 'test' from 'test.py'>

In [41]: a = test.UnboundInteger(1000000000000)

In [42]: b = test.UnboundInteger(20000000000)

In [43]: a + b
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-43-f96fb8f649b6> in <module>()
----> 1 a + b

/home/neel101/test.py in __add__(self, other)
     17             temp = '0' + temp
     18             temp = temp[-1]
---> 19             carry = temp[-2]
     20             result = temp + result
     21 

IndexError: string index out of range

如果你有更好的解决方案，也请告诉我！

Answer 1

这个问题发生是因为你在覆盖临时变量。

temp = '0' + temp
temp = temp[-1]
carry = temp[-2]

应该这样写：

temp = '0' + temp
carry = temp[-2]
temp = temp[-1]