TypeError: unhashable type: 'list' but I'm using a string as index?

I am having this error:

Traceback (most recent call last):
  File (...)
    edge = random.choice(graph[node])
TypeError: unhashable type: 'list'

My code is as follows:

print(graph) # {'0': ['3'], 
             # '1': ['0'], 
             # '2': ['1', '6'], 
             # '3': ['2'], 
             # '4': ['2'], 
             # '5': ['4'], 
             # '6': ['5', '8'], 
             # '7': ['9'], 
             # '8': ['7'], 
             # '9': ['6']}

visited = {}

node = random.choice(list(graph.keys()))
print(node) # '9' for example
# edge = random.choice(graph[node]) ---> this prints ['6'] but fails inside the loop
while True:
    edge = random.choice(graph[node]) # this is where it breaks

    if node not in visited:
        visited[node] = [edge]
    else:
        if visited[node] == edge:
            break
        else:
            visited[node].append(edge)

        if visited[node]==graph[node]:
            break

    node = graph[edge]

print(visited)

I've looked through other answers and they're all trying to index a dict with a list, but node is a string, which should work. The code right above the loop works, and I even tried with a different loop condition. I'm trying to get a random key and then get its value (trying to randomly walk in a directed graph). Thanks!