Tarjan's Algorithm for finding SCC in graph

Tarjans.py

def dfs(graph, node):
    global timer

    visited.add(node)

    timer += 1

    disc[node] = low[node] = timer
    inStack[node] = True
    st.append(node)

    for nei in graph[node]:
        if nei not in visited:
            dfs(graph, nei)
            low[node] = min(low[node], low[nei])
        elif nei in visited and inStack[nei]:
            low[node] = min(low[node], disc[nei])

    if disc[node] == low[node]:
        tmp = []

        while st and st[-1] != node:
            itm = st.pop()
            tmp.append(itm)
            inStack[itm] = False

        tmp.append(node)
        st.pop()

        res.append(tmp)


N = 7

graph = {
    1: [2],
    2: [3],
    3: [4],
    4: [2, 5],
    5: [6],
    6: [7],
    7: [6]
}

disc = {}
low = {}
inStack = {}
st = []
visited = set()

timer = 0

res = []

for i in range(1, N + 1):
    if i not in visited:
        dfs(graph, i)

print(res)