Buggy python submission (verdict: Time Limit Exceeded):
s=input()
t=input()
a=len(s)
b=len(t)
n_list=  ['' for i in range(a)]
b_list=['' for j in range(b)]
for i in range(b) :
  if s[0] in t[:i+1] :
    b_list[i]=s[0]
for i in range(a) :
  if t[0] in s[:i+1] :
    n_list[i]=t[0]

import copy
for i in range(1,b) :
  n_list1=copy.deepcopy(n_list)
  n_list[0]=b_list[i]
  for j in range(1,a) :
    
    if len(n_list1[j])>len(n_list[j]) :
      n_list[j]=n_list1[j]
    if len(n_list[j-1])>len(n_list[j]) :
      n_list[j]=n_list[j-1]
    if t[i]==s[j] and len(n_list1[j-1])+1>len(n_list[j])  :
      n_list[j] = n_list1[j - 1]+t[i]

print(n_list[-1])

Fixed submission:
s=input()
t=input()
a=len(s)
b=len(t)
n_list=  ['' for i in range(a)]
b_list=['' for j in range(b)]
for i in range(b) :
  if s[0] in t[:i+1] :
    b_list[i]=s[0]
for i in range(a) :
  if t[0] in s[:i+1] :
    n_list[i]=t[0]

import copy
for i in range(1,b) :
  n_list1=copy.copy(n_list)
  n_list[0]=b_list[i]
  for j in range(1,a) :

    if len(n_list1[j])>len(n_list[j]) :
      n_list[j]=n_list1[j]
    if len(n_list[j-1])>len(n_list[j]) :
      n_list[j]=n_list[j-1]
    if t[i]==s[j] and len(n_list1[j-1])+1>len(n_list[j])  :
      n_list[j] = n_list1[j - 1]+t[i]

print(n_list[-1])

Buggy python submission (verdict: Time Limit Exceeded):
s=input()
t=input()
a=len(s)
b=len(t)
n_list=  [['' for i in range(a)] for j in range(b)]
for i in range(b) :
  if s[0] in t[:i+1] :
    n_list[i][0]=s[0]
for i in range(a) :
  if t[0] in s[:i+1] :
    n_list[0][i]=t[0]


for i in range(1,b) :
  for j in range(1,a) :
    if len(n_list[i-1][j])>len(n_list[i][j]) :
      n_list[i][j]=n_list[i-1][j]
    if len(n_list[i][j-1])>len(n_list[i][j]) :
      n_list[i][j]=n_list[i][j-1]
    if t[i]==s[j] and len(n_list[i-1][j-1])+1>len(n_list[i][j])  :
      n_list[i][j] = n_list[i-1][j - 1]+t[i]

print(n_list[-1][-1])

Fixed submission:
s=input()
t=input()
a=len(s)
b=len(t)
n_list=  ['' for i in range(a)]
b_list=['' for j in range(b)]
for i in range(b) :
  if s[0] in t[:i+1] :
    b_list[i]=s[0]
for i in range(a) :
  if t[0] in s[:i+1] :
    n_list[i]=t[0]

import copy
for i in range(1,b) :
  n_list1=copy.copy(n_list)
  n_list[0]=b_list[i]
  for j in range(1,a) :

    if len(n_list1[j])>len(n_list[j]) :
      n_list[j]=n_list1[j]
    if len(n_list[j-1])>len(n_list[j]) :
      n_list[j]=n_list[j-1]
    if t[i]==s[j] and len(n_list1[j-1])+1>len(n_list[j])  :
      n_list[j] = n_list1[j - 1]+t[i]

print(n_list[-1])

Buggy python submission (verdict: Time Limit Exceeded):
x=input()
y=input()
x_part=[[]]*len(x)
y_part=[[]]*len(y)
x_part[0]=['',x[0]]
y_part[0]=['',y[0]]
x_part1=['',x[0]]
for i in range(1,len(x)) :
  part=[]
  for item  in x_part1 :
    part.append(item+x[i])
  x_part1.extend(part)
 
 
y_part1=['',y[0]]
for i in range(1,len(y)) :
  part=[]
  for item  in y_part1 :
    part.append(item + y[i])
  y_part1.extend(part)
 
 
 
common=list(set(x_part1)& set(y_part1))

 
current_length=0
current_word=''
for item in common :
  if len(item)>current_length :
    current_length=len(item)
    current_word=item
print(current_word)

Fixed submission:
s=input()
t=input()
a=len(s)
b=len(t)
n_list=  ['' for i in range(a)]
b_list=['' for j in range(b)]
for i in range(b) :
  if s[0] in t[:i+1] :
    b_list[i]=s[0]
for i in range(a) :
  if t[0] in s[:i+1] :
    n_list[i]=t[0]

import copy
for i in range(1,b) :
  n_list1=copy.copy(n_list)
  n_list[0]=b_list[i]
  for j in range(1,a) :

    if len(n_list1[j])>len(n_list[j]) :
      n_list[j]=n_list1[j]
    if len(n_list[j-1])>len(n_list[j]) :
      n_list[j]=n_list[j-1]
    if t[i]==s[j] and len(n_list1[j-1])+1>len(n_list[j])  :
      n_list[j] = n_list1[j - 1]+t[i]

print(n_list[-1])