PyCharm 中的“未解析的属性引用”

Question

我在 PyCharm 中收到 unresolved attribute reference 'get_opposite_node' for class 'list' 警告，即使代码运行良好。

这是代码的相关部分：

    def bfs(self, start, end):
        visited = {start}  # visited set contains int indices
        start_node = self.Node(start)
        q = deque()
        q.append(start_node)  # deque contains Node objects
        while q:
            cur_node = q.popleft()  # Node object
            if cur_node.idx == end:
                return cur_node 

            for edge in self.get_out_edges(cur_node):
                # HERE IS WHERE I GET THE WARNING:
                child = self.Node(edge.get_opposite_node(i))
                child_idx = child.idx
                if child_idx not in visited:
                    visited.add(child_idx)
                    q.append(child)
                    child.parent = cur_node
        return None

    def get_out_edges(self, node):
        return self.adj[node.idx]

    def add_edge(self, line):
        # line is just a string from the input file 
        (v, u, w) = [int(x) for x in line.split()]
        e = Edge(v,u,w)
        self.adj[v].append(e)
        self.adj[u].append(e)
        self.edges.append(e)

self.adj是列表的列表：self.adj = [[] for _ in range(N)]，后来被Edge类的边缘填充：

class Edge:
    def __init__(self, v, u, w):
        self.v = v
        self.u = u
        self.w = w

    def get_node(self):
        return self.v

    def get_opposite_node(self, k=None):
        return self.u if k == self.v or k is None else self.v

所以，基本上，虽然self.adj[i] 包含Edges，但 PyCharm 认为它包含列表（？）。有没有办法“说服”PyCharm 它不是这样的？

Answer 1

PyCharm 很困惑，因为您已将 adj 明确声明为（空）lists 的 list。它不能说您随后用理解get_opposite_node() 的对象覆盖了adj 的每个元素。但它确实知道您不能在 list 上使用 get_opposite_node()。

您可以通过将adj 声明为包含None 的list 而不是空的lists 的list 来解决此问题。下面可能会澄清一点：

class RealEdge:
    def get_something(self):
        return "something"


class SomeEdgyThing:
    def __init__(self, size):
        self.adj = [[] for _ in range(size)]


class SomeOtherEdgyThing:
    def __init__(self, size):
        self.adj = [None for _ in range(size)]


class ReallyEdgyThing:
    def __init__(self, size):
        self.adj = [RealEdge() for _ in range(size)]


my_complicated_thing = SomeEdgyThing(7)
for i in range(len(my_complicated_thing.adj)):
    my_complicated_thing.adj[i] = RealEdge()
# PyCharm warning:
#     Unresolved attribute reference 'get_something' for class 'list'
# Runs fine, because we overwrote all the values in adj
# with RealEdges instead of lists.
print(my_complicated_thing.adj[1].get_something())

my_thing = SomeEdgyThing(7)
try:
    # PyCharm warning:
    #     Unresolved attribute reference 'get_something' for class 'list'
    # Also a runtime error:
    #     AttributeError: 'list' object has no attribute 'get_something'
    print(my_thing.adj[1].get_something())
except AttributeError as e:
    print(e)

my_other_thing = SomeOtherEdgyThing(7)
try:
    # PyCharm doesn't complain.
    # Does it assume NoneType is part of a union type...?
    # Runtime error:
    #     AttributeError: 'NoneType' object has no attribute 'get_something'
    print(my_other_thing.adj[1].get_something())
except AttributeError as e:
    print(e)

real_thing = ReallyEdgyThing(7)
# No error
print(real_thing.adj[1].get_something())

输出：

something
'list' object has no attribute 'get_something'
'NoneType' object has no attribute 'get_something'
something

我怀疑你真的不需要写 self.adj = [[] for _ in range(N)] 并且 self.adj = [None for _ in range(N)] 也可以使用，并且会导致警告消失。

现在，您仍然会遇到这样的情况：您的代码以某种方式以错误的顺序运行，并且您尝试在 adj 的成员上调用 get_opposite_node()，而您尚未更新为包含真正的 Edge。你只是不再被警告了。出于这个原因，我建议将这些调用包装在 try: ... except AttributeError: 块中。