Buggy python submission (verdict: Time Limit Exceeded):
import copy
def hashnum(state):
    num = 0
    for i in range(3):
        for j in range(3):
            num *= 10
            num += state[i][j]
    return num

answer = 123456780
ini_state = []
for i in range(3):
    temp = [int(n) for n in input().split(" ")]
    if 0 in temp:
        zero_x, zero_y = temp.index(0), i
    ini_state.append(temp)
queue = [[ini_state, zero_x, zero_y]]
dx = [1, 0, -1, 0]
dy = [0, 1, 0, -1]
visited = set()
visited |= {hashnum(ini_state)}
trial = 0
while answer not in visited:
    new_queue = []
    for q in queue:
        state, zero_x, zero_y = q
        for i in range(len(dx)):
            new_state = copy.deepcopy(state)
            new_x = zero_x + dx[i]
            new_y = zero_y + dy[i]
            if 0 <= new_x < 3 and 0 <= new_y < 3:
                new_state[new_y][new_x], new_state[zero_y][zero_x] = new_state[zero_y][zero_x], new_state[new_y][new_x]
                perm = hashnum(new_state)
                if perm not in visited:
                    visited |= {perm}
                    new_queue.append([new_state, new_x, new_y])
    queue = new_queue
    trial += 1
print(trial)

Fixed submission:
import copy
def hashnum(state):
    num = 0
    for i in range(3):
        for j in range(3):
            num *= 10
            num += state[i][j]
    return num

answer = 123456780
ini_state = []
for i in range(3):
    temp = [int(n) for n in input().split(" ")]
    if 0 in temp:
        zero_x, zero_y = temp.index(0), i
    ini_state.append(temp)
end_state = [[1, 2, 3], [4, 5, 6], [7, 8, 0]]
queue = [[ini_state, zero_x, zero_y, 0], [end_state, 2, 2, 1]]
dx = [1, 0, -1, 0]
dy = [0, 1, 0, -1]
visited = {}
if hashnum(ini_state) == answer:
    print(0)
else:
    visited[hashnum(ini_state)] = [0, 0]
    visited[answer] = [0, 1]
    trial = 0
    ended = 0
    while queue:
        new_queue = []
        trial += 1
        for q in queue:
            if ended:
                break
            state, zero_x, zero_y, direction = q
            for i in range(len(dx)):
                new_state = copy.deepcopy(state)
                new_x = zero_x + dx[i]
                new_y = zero_y + dy[i]
                if 0 <= new_x < 3 and 0 <= new_y < 3:
                    new_state[new_y][new_x], new_state[zero_y][zero_x] = new_state[zero_y][zero_x], new_state[new_y][new_x]
                    perm = hashnum(new_state)
                    if perm in visited and direction != visited[perm][1]:
                        print(trial + visited[perm][0])
                        ended = 1
                        break
                    elif perm not in visited:
                        visited[perm] = [trial, direction]
                        new_queue.append([new_state, new_x, new_y, direction])
        queue = new_queue

Buggy python submission (verdict: Time Limit Exceeded):
import copy
def hashnum(state):
    num = 0
    for i in range(3):
        for j in range(3):
            num *= 10
            num += state[i][j]
    return num

answer = 123456780
ini_state = []
for i in range(3):
    temp = [int(n) for n in input().split(" ")]
    if 0 in temp:
        zero_x, zero_y = temp.index(0), i
    ini_state.append(temp)
queue = [[ini_state, zero_x, zero_y]]
dx = [1, 0, -1, 0]
dy = [0, 1, 0, -1]
visited = set()
visited |= {hashnum(ini_state)}
trial = 0
while answer not in visited:
    new_queue = []
    trial += 1
    for q in queue:
        state, zero_x, zero_y = q
        for i in range(len(dx)):
            new_state = copy.deepcopy(state)
            new_x = zero_x + dx[i]
            new_y = zero_y + dy[i]
            if 0 <= new_x < 3 and 0 <= new_y < 3:
                new_state[new_y][new_x], new_state[zero_y][zero_x] = new_state[zero_y][zero_x], new_state[new_y][new_x]
                perm = hashnum(new_state)
                if perm == answer:
                    print(trial)
                    exit()
                if perm not in visited:
                    visited |= {perm}
                    new_queue.append([new_state, new_x, new_y])
    queue = new_queue
    
# print(trial)

Fixed submission:
import copy
def hashnum(state):
    num = 0
    for i in range(3):
        for j in range(3):
            num *= 10
            num += state[i][j]
    return num

answer = 123456780
ini_state = []
for i in range(3):
    temp = [int(n) for n in input().split(" ")]
    if 0 in temp:
        zero_x, zero_y = temp.index(0), i
    ini_state.append(temp)
end_state = [[1, 2, 3], [4, 5, 6], [7, 8, 0]]
queue = [[ini_state, zero_x, zero_y, 0], [end_state, 2, 2, 1]]
dx = [1, 0, -1, 0]
dy = [0, 1, 0, -1]
visited = {}
if hashnum(ini_state) == answer:
    print(0)
else:
    visited[hashnum(ini_state)] = [0, 0]
    visited[answer] = [0, 1]
    trial = 0
    ended = 0
    while queue:
        new_queue = []
        trial += 1
        for q in queue:
            if ended:
                break
            state, zero_x, zero_y, direction = q
            for i in range(len(dx)):
                new_state = copy.deepcopy(state)
                new_x = zero_x + dx[i]
                new_y = zero_y + dy[i]
                if 0 <= new_x < 3 and 0 <= new_y < 3:
                    new_state[new_y][new_x], new_state[zero_y][zero_x] = new_state[zero_y][zero_x], new_state[new_y][new_x]
                    perm = hashnum(new_state)
                    if perm in visited and direction != visited[perm][1]:
                        print(trial + visited[perm][0])
                        ended = 1
                        break
                    elif perm not in visited:
                        visited[perm] = [trial, direction]
                        new_queue.append([new_state, new_x, new_y, direction])
        queue = new_queue