Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
import sys
sys.setrecursionlimit(10**9)
n=int(input())
g=[[] for i in range(n)]
for i in range(n-1):
    a,b=map(int,input().split())
    a-=1
    b-=1
    g[a].append(b)
    g[b].append(a)
q=deque([0])
v=[0]*n
v[0]=1
gp=[[] for i in range(n)]
while q:
    p=q.popleft()
    for i in g[p]:
        if v[i]==0:
            v[i]=1
            gp[p].append(i)
            q.append(i)
MOD=10**9+7
flag=[0]*n
dp=[[0,0] for i in range(n)]
def f(i):
    if flag[i]:
        return 0
    flag[i]=1
    dp[i][0]=1
    dp[i][1]=1
    for j in gp[i]:
        f(j)
        dp[i][0]=dp[i][0]*(dp[j][0]+dp[j][1])%MOD
        dp[i][1]=dp[i][1]*dp[j][0]
        dp[i][0]%=MOD
        dp[i][1]%=MOD
    return 0
f(0)
print((dp[0][0]+dp[0][1])%MOD)


Fixed submission:
from collections import deque
import sys
sys.setrecursionlimit(10**9)
n=int(input())
g=[[] for i in range(n)]
for i in range(n-1):
    a,b=map(int,input().split())
    a-=1
    b-=1
    g[a].append(b)
    g[b].append(a)
q=deque([0])
v=[0]*n
v[0]=1
gp=[[] for i in range(n)]
while q:
    p=q.popleft()
    for i in g[p]:
        if v[i]==0:
            v[i]=1
            gp[p].append(i)
            q.append(i)
MOD=10**9+7
flag=[0]*n
dp=[[0,0] for i in range(n)]
def f(i):
    if flag[i]:
        return 0
    flag[i]=1
    dp[i][0]=1
    dp[i][1]=1
    for j in gp[i]:
        f(j)
        dp[i][0]=dp[i][0]*(dp[j][0]+dp[j][1])%MOD
        dp[i][1]=dp[i][1]*dp[j][0]
        dp[i][0]%=MOD
        dp[i][1]%=MOD
    return 0
f(0)
print((dp[0][0]+dp[0][1])%MOD)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
import sys
sys.setrecursionlimit(10**9)
n=int(input())
g=[[] for i in range(n)]
for i in range(n-1):
    a,b=map(int,input().split())
    a-=1
    b-=1
    g[a].append(b)
    g[b].append(a)
q=deque([0])
v=[0]*n
v[0]=1
gp=[[] for i in range(n)]
while q:
    p=q.popleft()
    for i in g[p]:
        if v[i]==0:
            v[i]=1
            gp[p].append(i)
            q.append(i)
MOD=10**9+7
flag=[0]*n
dp=[[0,0] for i in range(n)]
def f(i):
    if flag[i]:
        return 0
    flag[i]=1
    dp[i][0]=1
    dp[i][1]=1
    for j in gp[i]:
        f(j)
        dp[i][0]=dp[i][0]*(dp[j][0]+dp[j][1])%MOD
        dp[i][1]=dp[i][1]*dp[j][0]
    return 0
f(0)
print((dp[0][0]+dp[0][1])%MOD)


Fixed submission:
from collections import deque
import sys
sys.setrecursionlimit(10**9)
n=int(input())
g=[[] for i in range(n)]
for i in range(n-1):
    a,b=map(int,input().split())
    a-=1
    b-=1
    g[a].append(b)
    g[b].append(a)
q=deque([0])
v=[0]*n
v[0]=1
gp=[[] for i in range(n)]
while q:
    p=q.popleft()
    for i in g[p]:
        if v[i]==0:
            v[i]=1
            gp[p].append(i)
            q.append(i)
MOD=10**9+7
flag=[0]*n
dp=[[0,0] for i in range(n)]
def f(i):
    if flag[i]:
        return 0
    flag[i]=1
    dp[i][0]=1
    dp[i][1]=1
    for j in gp[i]:
        f(j)
        dp[i][0]=dp[i][0]*(dp[j][0]+dp[j][1])%MOD
        dp[i][1]=dp[i][1]*dp[j][0]
        dp[i][0]%=MOD
        dp[i][1]%=MOD
    return 0
f(0)
print((dp[0][0]+dp[0][1])%MOD)

Buggy python submission (verdict: Runtime Error):
from collections import deque
n=int(input())
g=[[] for i in range(n)]
for i in range(n-1):
    a,b=map(int,input().split())
    a-=1
    b-=1
    g[a].append(b)
    g[b].append(a)
q=deque([0])
v=[0]*n
v[0]=1
gp=[[] for i in range(n)]
while q:
    p=q.popleft()
    for i in g[p]:
        if v[i]==0:
            v[i]=1
            gp[p].append(i)
            q.append(i)
MOD=10**9+7
flag=[0]*n
dp=[[0,0] for i in range(n)]
def f(i):
    if flag[i]:
        return 0
    flag[i]=1
    dp[i][0]=1
    dp[i][1]=1
    for j in gp[i]:
        f(j)
        dp[i][0]=dp[i][0]*(dp[j][0]+dp[j][1])%MOD
        dp[i][1]=dp[i][1]*dp[j][0]
    return 0
f(0)
print((dp[0][0]+dp[0][1])%MOD)

Fixed submission:
from collections import deque
import sys
sys.setrecursionlimit(10**9)
n=int(input())
g=[[] for i in range(n)]
for i in range(n-1):
    a,b=map(int,input().split())
    a-=1
    b-=1
    g[a].append(b)
    g[b].append(a)
q=deque([0])
v=[0]*n
v[0]=1
gp=[[] for i in range(n)]
while q:
    p=q.popleft()
    for i in g[p]:
        if v[i]==0:
            v[i]=1
            gp[p].append(i)
            q.append(i)
MOD=10**9+7
flag=[0]*n
dp=[[0,0] for i in range(n)]
def f(i):
    if flag[i]:
        return 0
    flag[i]=1
    dp[i][0]=1
    dp[i][1]=1
    for j in gp[i]:
        f(j)
        dp[i][0]=dp[i][0]*(dp[j][0]+dp[j][1])%MOD
        dp[i][1]=dp[i][1]*dp[j][0]
        dp[i][0]%=MOD
        dp[i][1]%=MOD
    return 0
f(0)
print((dp[0][0]+dp[0][1])%MOD)