bet_insert.py

def insert(self, expression: str):
      """
      Insert the postfix expression into the tree using stack
      """
      postfix_exp = self.infix_to_postfix(expression)
      # if max size is 0, then it is infinite
      stack = deque()
      char = postfix_exp[0]
      # create a node for the first element of the expression
      node = BinaryTreeNode(char)
      # push it to stack
      stack.appendleft(node)

      # iterator for expression
      i = 1
      while len(stack) != 0:
          char = postfix_exp[i]
          # if char is float or int
          if '.' in char or char.isdigit():
              # create a node and push the node into the stack
              node = BinaryTreeNode(char)
              stack.appendleft(node)
          else:
              # create a parent(operator) node for operands
              operator_node = BinaryTreeNode(char)
              operator_node.operator = True
              # pop the last pushed item and create right_child
              right_child = stack.popleft()
              # pop item one before the last item and create left_child
              left_child = stack.popleft()
              # assign those as a child of the (parent)operator
              operator_node.right = right_child
              operator_node.left = left_child
              # push back the operator node(subtree) to the stack
              stack.appendleft(operator_node)
              # check if we reach last element in the expression
              # so we can define the root of the tree
              if len(stack) == 1 and i == len(postfix_exp) - 1:
                  self.root = stack.popleft()
          # increment i
          i += 1
          self.size += 1
      print(f"i is {i} in insert ")