```
class Solution:
# @param root, a tree node
# @return an integer
def maxsum(self, root):
if root == None:
return 0
sum = root.val
lmax = self.maxsum(root.left)
rmax = self.maxsum(root.right)
if lmax > 0: sum += lmax;
if rmax > 0: sum += rmax;
Solution.max = max(Solution.max, sum)
return max(root.val, max(root.val + lmax, root.val + rmax))
def maxPathSum(self, root):
Solution.max = -10000000
if root == None:
return 0
self.maxsum(root)
return Solution.max
```

I was trying to set variable name Solution.max to max or best before, but OJ said variable doesn't define. It only works when Solution. something. Is it because of class name? Could someone explain to me? Thanks in advance!