python for i in List不能print出List中所有的值

  我复刻了您图片中的代码(未修改您的变量命名)，修正了变量a、b处的return ，改用了print() 。但您最后一条return 后面是字符串与list 相加，我用join()方法拼接了字符列表。您return 1、return 0那段，算起起来是接收多项式中的常量或x的一次方的，也应该赋值给变量而不可以用return关键字，没太弄明白，没作改动。

#!/usr/bin/nve python
# coding: utf-8

class ProcessDerivative:
    
    def __init__(self, polynomial):
        self.polynomial = polynomial


    def get_first_derivative(self):
        import re
        str1 = self.polynomial
        List = re.split('\+|-', str1)
        print(List)
        result_two = []

        for i in List:
            print(i)
            
            # import re # 不用重复加载re。
            list = re.split('\*|\^', i)

            if len(list) == 1 and int(list[0]) is False:
                return 1
            elif len(list) == 1 and int(list[0]) is True:
                return 0
            elif len(list) == 2: 
                try:
                    int(list[0])
                    return list[0]
                except:
                    a = str(int(list[1])) + '*' + str(int(list[0])) + '^' + str(int(list[1]) - 1)
                    print(a)
            else:
                b = str(int(list[2])*int(list[0])) + '*' + str(list[1]) + '^' + str(int(list[2])-1)
                print(b)

                result_two = list
        return 'The first derivative is: ' + ''.join(result_two) # e.g. The first derviative is: '6*x^2+6*x+5'"


if __name__ == '__main__':
    result = ProcessDerivative('3*x^3+2*x^2')
    print(result.get_first_derivative())

        result_two = List[0]
        return 'The first derivative is: ' + result_two # e.g. The first derviative is: '6*x^2+6*x+5'"

最最后那条return 语句，您应该是想得到这样子的效果。