Leetcode #7. Reverse Integer

class Solution:    def reverse(self, x):        """        :type x: int        :rtype: int        """        ret = 0        nega = 0 if x > 0 else 1                if nega:            x = -x                while x > 0:            ret = ret * 10 + x % 10            x //= 10                if nega:            ret = -ret        if ret.bit_length() >= 32:            return 0        return ret        

注意

int.bit_length()

Return the number of bits necessary to represent an integer in binary, excluding the sign and leading zeros:

>>>

>>> n = -37>>> bin(n)'-0b100101'>>> n.bit_length()6

More precisely, if x is nonzero, then x.bit_length() is the unique positive integer k such that 2**(k-1) <= abs(x) < 2**k. Equivalently, when abs(x) is small enough to have a correctly rounded logarithm, then k = 1 + int(log(abs(x), 2)). If x is zero, then x.bit_length() returns 0.

去除符号位，共有31位，即当bit_length大于等于32时，超出32位int表示范围。