[Python] Graph as dictionary of sets, how to iterate through neighbors (values in each set)

Trying to solve Leetcode problem 207. Course Schedule: https://leetcode.com/problems/course-schedule/description/

For this, I implemented a Graph as a dictionary of sets (sort of an adjacency list).

However my code throws

TypeError: unhashable type: 'set'


when I try to iterate through a node's neighbors on line

for i in reverseGraph[cur]:


class Solution:
def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:
# build adj list graph where a points to b
graph = {}
reverseGraph = {}
for i in range(0, numCourses):
graph = set()
reverseGraph = set()
for idx, prereq in enumerate(prerequisites):
graph[prereq[0]].add(prereq[1])
reverseGraph[prereq[1]].add(prereq[0])

print("graph: ", graph)
print("reverseGraph: ", reverseGraph)

# see if we can take all courses in graph
toRemoveStack = []
for i in range(0, numCourses):
if len(graph) == 0:
toRemoveStack.append(i)
print("toRemoveStack: ", toRemoveStack)
while len(toRemoveStack) > 0:
cur = toRemoveStack.pop()
for i in reverseGraph[cur]:
graph.remove(cur)
if len(graph) == 0:
toRemoveStack.append(graph)
del graph[cur]

return len(graph) == 0


How does one correctly iterate though the neighbors? And yes I know there are other solutions on Leetcode using different algorithms. I just want to figure out if this representation of a Graph in Python is good or if it will bite me in the ass in interviews.

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