Python TypeError问题：get_manhattan_distance()需2参数却传入3个

用户编写了计算角色位置到最近食物曼哈顿距离的代码，其中state结构为((x, y), ("some status"))，food_coords是网格坐标列表[(x, y), ...]。调用get_manhattan_distance(pos, food_pos)时触发错误：

TypeError: GridProblem.get_manhattan_distance() takes 2 positional arguments but 3 were given

注：调用时角色位置与食物处于同一网格位置。相关代码：

# helper function to calculate the manhattan distance
def get_manhattan_distance(p, q):
    distance = 0
    for p_i,q_i in zip(p,q):
        distance += abs(p_i - q_i)
    return distance

# heuristic = Manhattan distance
def h(self, node):
    if self.is_goal(node.state):
        return 0
    pos = node.state[0] #current position (x, y)
    x_coord = node.state[0][0]
    y_coord = node.state[0][1]
    distances = []
    for food_pos in self.food_coords:
        print('pos=',pos)
        print('food_pos=',pos)
        distances.append(self.get_manhattan_distance(pos, food_pos))
    distances.sort()
    return distances[0]

核心错误原因 #

get_manhattan_distance是普通全局函数，但在h方法中用self.get_manhattan_distance(pos, food_pos)调用时，会自动把self作为第一个参数传入，导致实际传递了3个参数（self、pos、food_pos），但函数定义只接受2个参数（p、q），触发参数不匹配错误。

此外代码还有一处打印错误：print('food_pos=',pos)应该输出food_pos变量，而非pos。

两种修复方案 #

方案1：将全局函数改为类方法 #

给get_manhattan_distance添加self参数，使其成为类的成员方法：

# 修改为类方法，添加self参数
def get_manhattan_distance(self, p, q):
    distance = 0
    for p_i,q_i in zip(p,q):
        distance += abs(p_i - q_i)
    return distance

# heuristic = Manhattan distance
def h(self, node):
    if self.is_goal(node.state):
        return 0
    pos = node.state[0] #current position (x, y)
    distances = []
    for food_pos in self.food_coords:
        print('pos=',pos)
        print('food_pos=',food_pos) # 修复打印错误
        distances.append(self.get_manhattan_distance(pos, food_pos))
    distances.sort()
    return distances[0]

方案2：直接调用全局函数 #

去掉调用时的self.前缀，直接使用函数名调用：

# helper function to calculate the manhattan distance
def get_manhattan_distance(p, q):
    distance = 0
    for p_i,q_i in zip(p,q):
        distance += abs(p_i - q_i)
    return distance

# heuristic = Manhattan distance
def h(self, node):
    if self.is_goal(node.state):
        return 0
    pos = node.state[0] #current position (x, y)
    distances = []
    for food_pos in self.food_coords:
        print('pos=',pos)
        print('food_pos=',food_pos) # 修复打印错误
        distances.append(get_manhattan_distance(pos, food_pos)) # 去掉self.
    distances.sort()
    return distances[0]

额外优化建议 #

• 可以用min()直接获取最小距离，省去排序后取第一个的步骤，简化代码：

  return min(get_manhattan_distance(pos, fp) for fp in self.food_coords)
  

• 代码中x_coord和y_coord变量未使用，可以删除。

内容的提问来源于stack exchange，提问作者Moe