```
class Solution:
# @return a list of lists of integers
def generate(self, numRows):
def sum2(prev_l, numRows):
if numRows == 0:
return
prev_l.insert(0,0)
prev_l.append(0)
new_l = []
for i in range(len(prev_l) - 1) :
new_l.append(prev_l[i] + prev_l[i+1])
prev_l.remove(0)
prev_l.pop()
result_l.append(new_l)
sum2(new_l, numRows - 1)
if numRows <= 0:
return []
elif numRows == 1:
return [[1]]
result_l = []
init_l = [1]
result_l.append(init_l)
sum2(init_l, numRows - 1)
return result_l
```

My accept code for Pascal's Triangle, by python, a little long.