python - 函数给出错误 ValueError : list. remove(x): x not in list

Question

我正在制作一个程序来寻找最近的房子和房子列表的过程。这 3 个函数用于查找类(class)，当我去打印结果时，最后给出了错误:

File "C:/Users/ASUS/.spyder-py3/tp_1.py", line 88, in percurso
  Casas.remove(pos_i)

ValueError: list.remove(x): x not in list

def distancia_casas(P1, P2):
    "returns distance between points"
    delta_x = P2[0] - P1[0]
    delta_y = P2[1] - P1[1]
    distance = ((delta_x ** 2) + (delta_y ** 2)) ** 0.5
    return distance

def casa_mais_proxima(P, Casas):

    pos_inicial = Casas[0]
    pos_mini = (len(Casas), len(Casas))
    dist_mini = distancia_casas(P, pos_mini)

    for c in Casas:
        dist = distancia_casas(P, c)

        if dist < dist_mini:
            pos_mini = c
            dist_mini = dist

        elif dist == dist_mini and pos_inicial[0] > c[0]:
            pos_mini = pos_inicial

        elif dist == dist_mini and pos_inicial[0] < c[0]:
            pos_mini = c

        elif dist == dist_mini and pos_inicial[0] == c[0] and pos_inicial[1] > c[1]:
            pos_mini = pos_inicial

        elif dist == dist_mini and pos_inicial[0] == c[0] and pos_inicial[1] < c[1]:
            pos_mini = c

        elif dist >  dist_mini:
            pos_mini = pos_mini

        else:
            pos_mini = c

    return pos_mini

def percurso(Inicial, Casas):

    pos_i = Inicial

    course = [pos_i,]

    n = len(Casas) - 1

    for c in range(n):
        print(pos_i, Casas)

        pos_i = casa_mais_proxima(pos_i, Casas)

        Casas.remove(pos_i)

        course.append(pos_i)

    if (len(Casas) - 1) != 0:

        course.append(Casas[0])

    return course

print("percurso", percurso((3,2),[(0,1),(1,0),(1,2),(2,3)]))

谁能帮帮我？我已经为此苦苦挣扎了 3 天，却一无所获

Answer 1

您不应该在遍历列表时从列表中删除项目。如错误消息所述，您正在尝试删除不存在的元素。因此:

1. 您可以使用列表理解来创建一个仅包含您要删除的元素的新列表:

   no_casas = []
   for c in range(n):
       print(pos_i, Casas)
   
       pos_i = casa_mais_proxima(pos_i, Casas)
   
       no_casas.append(pos_i)
   
       course.append(pos_i)
   
   for item in no_casas:
       Casas.remove(item)
   

但是，这种方法也会导致相同的异常，因为 casa_mais_proxima 可以多次返回 Casa 中的相同元素(这是该函数的预期行为吗？ )

因此:

1. 您可以使用Try/Except ValueError:

   try:
       Casas.remove(pos_i)
       course.append(pos_i)
   
   
   except ValueError:
       print(str(pos_i) + " not in Casas")
   

输出:

(3, 2) [(0, 1), (1, 0), (1, 2), (2, 3)]
(2, 3) [(0, 1), (1, 0), (1, 2)]
(3, 3) not in Casas
(3, 3) [(0, 1), (1, 0), (1, 2)]
(3, 3) not in Casas
percurso [(3, 2), (2, 3), (2, 3), (3, 3), (3, 3), (0, 1)]