def buildParseTree(fpexp):
exp_list = fpexp.split() # split the expression in a list wth the delimateur being space
stack = Stack()
current_node = BinaryTree('')
tokens = ['+', '-', '/', '*']
#stack.push(current_node)
for char in exp:
if char == '(':
current_node.insertLeft('')
S.push(current_node) # push parent into the stack
current_node = current_node.leftChild
elif char.isdigit():
current_node.key = int(char)
current_node = S.pop()
elif char in tokens:
current_node.insertRight('')
current_node.key = char
S.push(current_node)
current_node = current_node.rightChild
elif char == ')':
current_node = S.pop()
else:
raise ValueError
