comefrom: <doocs>0606.Construct String from Binary Tree_1.py
code: def dfs(root):
      if root is None:
          return ''
      if root.left is None and root.right is None:
          return str(root.val)
      if root.right is None:
          return f'{root.val}({dfs(root.left)})'
      return f'{root.val}({dfs(root.left)})({dfs(root.right)})'
masked: def sample_funcname ( var_0 ) :
      if var_0 is None :
          return ''
      if var_0.left is None and var_0.right is None :
          return str ( var_0.val )
      if var_0.right is None :
          return f'{var_0.val}({dfs(var_0.left)})'
      return f'{var_0.val}({dfs(var_0.left)})({dfs(var_0.right)})'
  