RPNCalculator

"""
Engine class of the RPN Calculator
"""

import math


class RPNEngine:
  def __init__(self):
    """ Constructor """
    self.stack = []
    self.catalog = self.get_functions_catalog()

  def get_functions_catalog(self):
    """ Returns the catalog of all the functions supported by the calculator """
    return {"+": (2, lambda x, y: x + y),
            "-": (2, lambda x, y: x - y),
            "*": (2, lambda x, y: x * y),
            "/": (2, lambda x, y: x / y),
            "^2": (1, lambda x: x * x),
            "SQRT": (1, math.sqrt),
            "C": (0, lambda: self.stack.pop()),
            "AC": (0, lambda: self.stack.clear())}

  def push(self, number):
    """ push a value to the internal stack """
    self.stack.append(number)

  def pop(self):
    """ pop a value from the stack """
    try:
      return self.stack.pop()
    except IndexError:
      pass  # do not notify any error if the stack is empty...

  def compute(self, operation):
    """ compute an operation """
    op_arity, op_func = self.catalog[operation]

    if len(self.stack) >= op_arity:
      op_args = []
      for _ in range(op_arity):
        op_args.insert(0, self.stack.pop())  # Insert at front to preserve stack order
      result = op_func(*op_args)
      self.push(result)
    else:
      print("Not enough operands on the stack")