trees print(root eval() if __name__ ="__main__"main(in sect the tree is built from the bottom ( the leavesup to the root the code above contains an eval function for each node calling eval on the root node will recursively call eval on every node in the treecausing the result to be printed to the screen once an ast is builtevaluating such tree is accomplished by doing recursive traversal of the tree the eval methods together are the recursive function in this example we say that the eval methods are mutually recursive since all the eval methods together form the recursive function prefix and postfix expressions expressionsas we normally write themare said to be in infix form an infix expression is an expression written with the binary operators in between their operands expressions can be written in other forms though another form for expressions is postfix in postfix expression the binary operators are written after their operands the infix expression ( can be written in postfix form as postfix expressions are well-suited for evaluation with stack when we come to an operand we push the value on the stack when we come to an operatorwe pop the operands from the stackdo the operationand push the result evaluating expressions in this manner is quite easy for humans to do with little practice hewlett-packard has designed many calculators that use this postfix evaluation method in factin the early years of computinghewlett-packard manufactured whole line of computers that used stack to evaluate expressions in the same way the hp was one such computer in more recent times many virtual machines are implemented as stack machines including the java virtual machineor jvmand the python virtual machine as another example of tree traversalconsider writing method that returns string representation of an expression the string is built as the result of traversal of the abstract syntax tree to get string representing an infix version of the expressionyou perform an inorder traversal of the ast to get postfix expression you would do postfix traversal of the tree the inorder methods in sect perform an inorder traversal of an ast ast tree traversal class timesnodedef __init__(selfleftright)self left left self right right this copy belongs to 'acha