题目：输入一个整数，求该整数的二进制表达中有多少个1。例如输入10，由于其二进制表示为1010，有两个1，因此输出2

解法:

#!/usr/bin/pythondef NumberOf1(n):    count = 0    while n:        if n & 1:            count += 1        n = n >> 1    return countdef NunberOf1A(n):    count = 0    while n:        count += 1        n = (n-1) & n    return count# different from c, it won't stop correctlydef NumberOf1B(n):    count = 0    flag = 1    while flag:        if n & flag:            count += 1        flag = flag << 1    return countdef main():    number = 9    print NumberOf1(number)    print NunberOf1A(number)    print NumberOf1B(number)    if __name__ == '__main__':    main()