Circle check in a weighted directed graph

circle_check.py

def circle_check(graph):
    n = len(graph)
    graph = [list(node.keys()) for node in graph]
    indexes = [0] * n
    stack = [0]
    visited = [False] * n
    visited[0] = True

    while stack:
        curr = stack[-1]
        while stack and len(graph[curr]) == indexes[curr]:
            visited[curr] = False
            stack.pop()
            if stack:
                curr = stack[-1]
        if not stack:
            break
        neigh = graph[curr][indexes[curr]]
        indexes[curr] += 1
        if visited[neigh]:
            return True
        visited[neigh] = True
        stack.append(neigh)

    return False