为什么当我试图将一个列表加入到一个字符串时会出现类型错误？

Question

我正试图用Python构建一个线性方程计算器。在通过询问用户问题来收集信息之后，我开始计算公式。如果用户说他们有两个点，通过这条线，我用这个信息来创建一个等式。方程的不同部分(例如斜率、y截距、操作、x和y)存储在一个列表中。在计算了这个方程之后，我想把这个列表加入到一个字符串中；但是，我得到了一个类型错误。以下是回溯的一部分：

File "/Users/matthewschell/PycharmProjects/Linear Equation Calculator/main.py", line 19, in slope_intercept
    final_equation = solve_slopeint(**arg_dict)
  File "/Users/matthewschell/PycharmProjects/Linear Equation Calculator/solve_functions.py", line 52, in solve_slopeint
    final_equation = ''.join(equation)
TypeError: sequence item 0: expected str instance, int found

下面是计算方程的函数的完整代码：

def solve_slopeint(**kwargs):
    if kwargs['point1'] is not None and kwargs['point2'] is not None:
        equation = [None, '= ']
        point1 = kwargs['point1']
        point2 = kwargs['point2']
        slope = (point2[1] - point1[1]) / (point2[0] - point1[0])
        slope = str(slope)

        if slope[-2:] == ".0":
            slope = str(int(float(slope)))
            num = 0  # Variable that lets program know the type of num the slope is. 0 = whole num and 1 = fraction
        else:
            num = point2[1] - point1[1]
            denom = point2[0] - point1[0]
            common_divisor = gcd(num, denom)
            numerator = num / common_divisor
            denominator = denom / common_divisor
            slope = [int(numerator), int(denominator)]
            num = 1

        equation.append(slope)
        equation.append(None)
        equation.append('+ ')
        equation.append(0)
        equation[0] = point1[1]
        equation[3] = point1[0]

        if num == 0:
            check = slope * equation[3]
            while check + equation[5] != equation[0]:
                if check + equation[5] < equation[0]:
                    equation[5] += 1

                elif check + equation[5] > equation[0]:
                    equation[5] -= 1

        else:
            check = (slope[0] * equation[3]) / slope[1]
            while check + equation[5] != equation[0]:
                if check + equation[5] < equation[0]:
                    equation[5] = equation[0] - (check + equation[5])

                elif check + equation[5] > equation[0]:
                    equation[5] = (check + equation[5]) - equation[0]

        for item in equation:
            item = str(item)
            print(item)

        final_equation = ''.join(equation)
        return final_equation

有人知道我为什么会出现类型错误吗？

Answer 1

在这个片段的这一部分：

        for item in equation:
            item = str(item)
            print(item)

您只对循环中存在的新项进行str()，而不是将它们保存在等式中。

        newequation = []
        for item in equation:
            newequation.append(str(item))
        equation = newequation

也许有更干净的方法来解决这个问题，但我不是很好