Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys, itertools

def WarshallFloyd(V: int, cost: "List[List[int]]"):
    """
    全ての頂点対の間の最短距離を求めます。
    ==============
    V: 頂点数
    cost: 隣接行列(辺が存在しない部分はINF)
    --------------
    cost: 最短距離の行列
    """
    for k in range(V):
        for i in range(V):
            for j in range(V):
                cost[i][j] = min(cost[i][j], cost[i][k] + cost[k][j])
    return cost

def solve(N: int, M: int, R: int, r: "List[int]", A: "List[int]", B: "List[int]", C: "List[int]"):
    INF = 1e18
    G = [[INF for _ in range(N)] for _ in range(N)]
    for i in range(M):
        G[A[i]-1][B[i]-1] = C[i]
        G[B[i]-1][A[i]-1] = C[i]
    cost = WarshallFloyd(N, G)
    mn = 1e18
    for p in itertools.permutations(r):
        path = 0
        for i in range(R-1):
            path += cost[p[i+1]-1][p[i]-1]
        mn = min(path, mn)
    print(mn)
    return


# Generated by 1.1.5 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    M = int(next(tokens))  # type: int
    R = int(next(tokens))  # type: int
    r = [int(next(tokens)) for _ in range(R)]  # type: "List[int]"
    A = [int()] * (M)  # type: "List[int]"
    B = [int()] * (M)  # type: "List[int]"
    C = [int()] * (M)  # type: "List[int]"
    for i in range(M):
        A[i] = int(next(tokens))
        B[i] = int(next(tokens))
        C[i] = int(next(tokens))
    solve(N, M, R, r, A, B, C)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys, itertools

def WarshallFloyd(V: int, cost: "List[List[int]]"):
    """
    全ての頂点対の間の最短距離を求めます。
    ==============
    V: 頂点数
    cost: 隣接行列(辺が存在しない部分はINF)
    --------------
    cost: 最短距離の行列
    """
    for k in range(V):
        for i in range(V):
            for j in range(V):
                cost[i][j] = min(cost[i][j], cost[i][k] + cost[k][j])
    return cost

def solve(N: int, M: int, R: int, r: "List[int]", A: "List[int]", B: "List[int]", C: "List[int]"):
    INF = 1e18
    G = [[INF for _ in range(N)] for _ in range(N)]
    for i in range(M):
        G[A[i]-1][B[i]-1] = C[i]
        G[B[i]-1][A[i]-1] = C[i]
    cost = WarshallFloyd(N, G)
    mn = 1e18
    for p in itertools.permutations(r):
        path = 0
        for i in range(R-1):
            path += cost[p[i+1]-1][p[i]-1]
        mn = min(path, mn)
    print(mn)
    return


# Generated by 1.1.5 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    M = int(next(tokens))  # type: int
    R = int(next(tokens))  # type: int
    r = [int(next(tokens)) for _ in range(R)]  # type: "List[int]"
    A = [int()] * (M)  # type: "List[int]"
    B = [int()] * (M)  # type: "List[int]"
    C = [int()] * (M)  # type: "List[int]"
    for i in range(M):
        A[i] = int(next(tokens))
        B[i] = int(next(tokens))
        C[i] = int(next(tokens))
    solve(N, M, R, r, A, B, C)

if __name__ == '__main__':
    main()