parse_tree.py

from stack_copy import Stack
from binary_tree_class import BinaryTree
import operator


def buildParseTree(fpexp):
    fplist = fpexp.split()
    pStack = Stack()
    eTree = BinaryTree('')
    pStack.push(eTree)
    currentTree = eTree

    for i in fplist:
        if i == '(':
            currentTree.insertLeft('')
            pStack.push(currentTree)
            currentTree = currentTree.getLeftChild()

        elif i in ['+', '-', '*', '/']:
            currentTree.setRootVal(i)
            currentTree.insertRight('')
            pStack.push(currentTree)
            currentTree = currentTree.getRightChild()

        elif i == ')':
            currentTree = pStack.pop()

        elif i not in ['+', '-', '*', '/', ')']:
            try:
                currentTree.setRootVal(int(i))
                parent = pStack.pop()
                currentTree = parent

            except ValueError:
                raise ValueError("token '{}' is not a valid integer".format(i))

    return eTree


def evaluate(parseTree):
    opers = {'+': operator.add, '-': operator.sub, '*': operator.mul, '/': operator.truediv}

    leftC = parseTree.getLeftChild()
    rightC = parseTree.getRightChild()

    if leftC and rightC:
        fn = opers[parseTree.getRootVal()]
        return fn(evaluate(leftC), evaluate(rightC))
    else:
        return parseTree.getRootVal()


pt = buildParseTree("( ( 10 + 5 ) * 3 )")
# pt.postorder()  #defined and explained in the next section