Buggy python submission (verdict: Runtime Error):
#EDP-F
import sys

S = sys.stdin.readline().rstrip()
T = sys.stdin.readline().rstrip()
sn, tn = len(S), len(T)
dp = [[0 for j in range(tn)] for i in range(sn)]

#方針:その時点での最長数を入れる
for j in range(tn):
    dp[0][j] = dp[0][j-1]
    if S[0]==T[j]:
        dp[0][j] = 1
for i in range(sn):
    dp[i][0] = dp[i-1][0]
    if S[i]==T[0]:
        dp[i][0] = 1
        

for i in range(1, sn):
    for j in range(1, tn):
        if S[i] == T[j]:
            dp[i][j] = dp[i-1][j-1]+1
        else:
            dp[i][j] = max(dp[i-1][j], dp[i][j-1])

#pprint.pprint(dp)

i,j= sn-1, tn-1
ans =''
while True:
    if i ==0:
        if dp[i][j]==1:
            ans+= S[0]
        print(ans[::-1])
        break
    if dp[i-1][j] == dp[i][j]:
        i-=1
    elif dp[i][j-1] == dp[i][j]:
        j-=1
    elif dp[i-1][j-1] +1 == dp[i][j]:
        ans += S[i]
        i-=1
        j-=1

Fixed submission:
import sys
s = sys.stdin.readline().rstrip()
t = sys.stdin.readline().rstrip()

sn = len(s)
tn = len(t)

dp =[[0 for _ in range(tn+1)] for _ in range(sn+1)]

for i in range(sn):
    for j in range(tn):
        if s[i]==t[j]:
            dp[i+1][j+1] =dp[i][j]+1
        else:
            dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1])
#print(dp)

L =[]
while sn>0 and tn>0:
    if dp[sn][tn] == dp[sn-1][tn]: #縦優先
        sn-=1
    elif dp[sn][tn] == dp[sn][tn-1]:
        tn-=1
    elif dp[sn][tn] == dp[sn-1][tn-1]+1:
        L.append(s[sn-1])
        sn-=1
        tn-=1
        
print(''.join(L[::-1]))

Buggy python submission (verdict: Time Limit Exceeded):
import sys
s = sys.stdin.readline().rstrip()
t = sys.stdin.readline().rstrip()

sn = len(s)
tn = len(t)

dp =[[0 for _ in range(tn+1)] for _ in range(sn+1)]

for i in range(sn):
    for j in range(tn):
        if s[i]==t[j]:
            dp[i+1][j+1] =dp[i][j]+1
        else:
            dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1])
#print(dp)

L =[]
while sn>0 and tn>0:
    if dp[sn][tn] == dp[sn-1][tn]: #縦優先
        sn-=1
    elif dp[sn][tn] == dp[sn][tn-1]:
        tn-=1
    elif dp[sn][tn] == dp[sn-1][tn-1]+1:
        L.append(s[sn-1])
        sn-=1
        tn-=1
        
print(''.join(L[::-1]))

Fixed submission:
import sys
s = sys.stdin.readline().rstrip()
t = sys.stdin.readline().rstrip()

sn = len(s)
tn = len(t)

dp =[[0 for _ in range(tn+1)] for _ in range(sn+1)]

for i in range(sn):
    for j in range(tn):
        if s[i]==t[j]:
            dp[i+1][j+1] =dp[i][j]+1
        else:
            dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1])
#print(dp)

L =[]
while sn>0 and tn>0:
    if dp[sn][tn] == dp[sn-1][tn]: #縦優先
        sn-=1
    elif dp[sn][tn] == dp[sn][tn-1]:
        tn-=1
    elif dp[sn][tn] == dp[sn-1][tn-1]+1:
        L.append(s[sn-1])
        sn-=1
        tn-=1
        
print(''.join(L[::-1]))

Buggy python submission (verdict: Time Limit Exceeded):
import sys
s = sys.stdin.readline().rstrip()
t = sys.stdin.readline().rstrip()

S = len(s)
T = len(t)

dp = [[0 for _ in range(T+1)] for _ in range(S+1)]


for i in range(S):
    for j in range(T):
        if s[i] ==t[j]:
            dp[i+1][j+1] = dp[i][j]+1
        else:
            dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1])
'''
for i in rage(S+1):
    print(dp[i])
'''

L =[]
while S>0 and T>0:
    if dp[S][T] != dp[S-1][T-1]+1:
        if dp[S][T] !=dp[S-1][T]:
            T-=1
        else:
            S-=1
    else:
        L.append(s[S-1])
        S-=1
        T-=1
print(''.join(L[::-1]))

Fixed submission:
import sys
s = sys.stdin.readline().rstrip()
t = sys.stdin.readline().rstrip()

sn = len(s)
tn = len(t)

dp =[[0 for _ in range(tn+1)] for _ in range(sn+1)]

for i in range(sn):
    for j in range(tn):
        if s[i]==t[j]:
            dp[i+1][j+1] =dp[i][j]+1
        else:
            dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1])
#print(dp)

L =[]
while sn>0 and tn>0:
    if dp[sn][tn] == dp[sn-1][tn]: #縦優先
        sn-=1
    elif dp[sn][tn] == dp[sn][tn-1]:
        tn-=1
    elif dp[sn][tn] == dp[sn-1][tn-1]+1:
        L.append(s[sn-1])
        sn-=1
        tn-=1
        
print(''.join(L[::-1]))