Coding dojo session result from 2019-03-14

reversed.py

"""
See https://www.codewars.com/kata/reverse-polish-notation-calculator

Your job is to create a calculator which evaluates expressions in Reverse Polish notation.
For example expression 5 1 2 + 4 * + 3 - (which is equivalent to 5 + ((1 + 2) * 4) - 3 in normal notation) should evaluate to 14.
For your convenience, the input is formatted such that a space is provided between every token.
Empty expression should evaluate to 0.
Valid operations are +, -, *, /.
You may assume that there won't be exceptional situations (like stack underflow or division by zero).
"""
from operator import add, sub, truediv, mul


class Node(object):
    def __init__(self, val):
        self.val = val

    def evaluate(self):
        return self.val


class OpNode(object):
    def __init__(self, op, a, b):
        self.op = op
        self.a = a
        self.b = b

    def evaluate(self):
        res_a = self.a.evaluate()
        res_b = self.b.evaluate()
        if self.op == '+':
            return res_a + res_b
        if self.op == '-':
            return res_a - res_b
        if self.op == '*':
            return res_a * res_b
        if self.op == '/':
            return float(res_a) / res_b
        else:
            raise RuntimeError('i am a dumb')


def parse_expr(tokens):
    next_token = tokens.pop()
    if next_token not in set('*-/+'):
        val = int(next_token) if next_token.isdigit() else float(next_token)
        return Node(val)
    else:
        op = next_token
        b = parse_expr(tokens)
        a = parse_expr(tokens)
        return OpNode(op, a, b)


op_map = {'+': add, '-': sub, '*': mul, '/': truediv}


def parse_expr_no_classes(tokens):
    next_token = tokens.pop()
    if next_token not in set('*-/+'):
        val = int(next_token) if next_token.isdigit() else float(next_token)
        return val
    else:
        op = next_token
        b = parse_expr_no_classes(tokens)
        a = parse_expr_no_classes(tokens)
        return op_map[op](a, b)


def calc(expr):
    """
    >>> calc("")
    0
    >>> calc("3")
    3
    >>> calc("3.5")
    3.5
    >>> calc("1 3 +")
    4
    >>> calc("1 3 *")
    3
    >>> calc("1 3 -")
    -2
    >>> calc("4 2 /")
    2
    >>> calc("5 1 2 + 4 * + 3 -")
    14
    >>> calc("1 2 + 3 * 4 - 5 /")
    1
    """
    if not expr:
        return 0

    tokens = expr.split(' ')
    res = parse_expr_no_classes(tokens)
    if res % 1 == 0:
        return int(res)
    return res