Buggy python submission (verdict: Runtime Error):
n, m = list(map(int, input().split()))
AB = [[int(x) for x in input().split()] for _ in range(m)]

# representation matrix
repn = [[] for j in range(n)]
for a, b in AB:
    a -= 1
    b -= 1
    repn[a].append(b)
    repn[b].append(a)


# Minimum Spanning Tree
tree = [[] for i in range(n)]
visited = [True] + [False] * (n - 1)
q = [0]

while q:
    u = q.pop()
    for v in repn[u]:
        if visited[v]:
            continue
        visited[v] = True
        tree[u].append(v)
        tree[v].append(u)
        q.append(v)


# define directions of the edges other than that of MST
degree = [0] * n
ans = []

for a, b in AB:
    a -= 1
    b -= 1
    if b in tree[a]:
        continue
    ans.append('{} {}'.format(a + 1, b + 1))
    degree[a] += 1


# defining orientations
def dfs(u = 0, parent = None):
    for v in tree[u]:
        if v == parent:
            continue
        dfs(v, u)
        if degree[v] % 2 == 0:
            ans.append('{} {}'.format(u + 1, v + 1))
            degree[u] += 1
        else:
            ans.append('{} {}'.format(v + 1, u + 1))
            degree[v] += 1

dfs()


# output answer
if degree[0] % 2 == 1:
    print(-1)
else:
    print('\n'.join(ans))


Fixed submission:
from collections import deque

N = int(input())
A = deque(map(int, input().split()))
first = A.popleft()


def round(a):
        B = list(A)
        eval = 0
        pre = first
        post = a
        B.remove(a)
        num = N - 2
        while num != 0:
                c = pre ^ post
                try:
                        B.remove(c)
                        pre = post
                        post = c
                        num -= 1
                except:
                        return 0
                        eval = 1
                        break
        
        if eval == 0 and post ^ first == a:
                return 1
        elif eval == 0:
                return 0

val = first
for i in range(N - 1):
        val = val ^ A[i]

if val != 0:
        print('No')
else:
        ans = 0
        for i in range(0, N - 1):
                ans = round(A[i])
                if ans == 1:
                        print('Yes')
                        break
                        

        if ans == 0:
                print('No')

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

N = int(input())
A = deque(map(int, input().split()))
first = A.popleft()


def round(a):
        B = list(A)
        eval = 0
        pre = first
        post = a
        B.remove(a)
        while len(B) != 0:
                c = pre ^ post
                try:
                        B.remove(c)
                        pre = post
                        post = c
                except:
                        return 0
                        eval = 1
                        break
        
        if eval == 0 and post ^ first == a:
                return 1
        elif eval == 0:
                return 0

ans = 0

for i in range(0, N - 1):
        ans = round(A[i])
        if ans == 1:
                print('Yes')
                break
                

if ans == 0:
        print('No')




Fixed submission:
from collections import deque

N = int(input())
A = deque(map(int, input().split()))
first = A.popleft()


def round(a):
        B = list(A)
        eval = 0
        pre = first
        post = a
        B.remove(a)
        num = N - 2
        while num != 0:
                c = pre ^ post
                try:
                        B.remove(c)
                        pre = post
                        post = c
                        num -= 1
                except:
                        return 0
                        eval = 1
                        break
        
        if eval == 0 and post ^ first == a:
                return 1
        elif eval == 0:
                return 0

val = first
for i in range(N - 1):
        val = val ^ A[i]

if val != 0:
        print('No')
else:
        ans = 0
        for i in range(0, N - 1):
                ans = round(A[i])
                if ans == 1:
                        print('Yes')
                        break
                        

        if ans == 0:
                print('No')