data_structures.stacks.postfix_evaluation
=========================================

.. py:module:: data_structures.stacks.postfix_evaluation

.. autoapi-nested-parse::

   Reverse Polish Nation is also known as Polish postfix notation or simply postfix
   notation.
   https://en.wikipedia.org/wiki/Reverse_Polish_notation
   Classic examples of simple stack implementations.
   Valid operators are +, -, *, /.
   Each operand may be an integer or another expression.

   Output:

   Enter a Postfix Equation (space separated) = 5 6 9 * +
    Symbol  |    Action    | Stack
   -----------------------------------
          5 | push(5)      | 5
          6 | push(6)      | 5,6
          9 | push(9)      | 5,6,9
            | pop(9)       | 5,6
            | pop(6)       | 5
          * | push(6*9)    | 5,54
            | pop(54)      | 5
            | pop(5)       |
          + | push(5+54)   | 59

           Result =  59



Attributes
----------

.. autoapisummary::

   data_structures.stacks.postfix_evaluation.OPERATORS
   data_structures.stacks.postfix_evaluation.UNARY_OP_SYMBOLS
   data_structures.stacks.postfix_evaluation.expression


Functions
---------

.. autoapisummary::

   data_structures.stacks.postfix_evaluation.evaluate
   data_structures.stacks.postfix_evaluation.parse_token


Module Contents
---------------

.. py:function:: evaluate(post_fix: list[str], verbose: bool = False) -> float

   Evaluate postfix expression using a stack.
   >>> evaluate(["0"])
   0.0
   >>> evaluate(["-0"])
   -0.0
   >>> evaluate(["1"])
   1.0
   >>> evaluate(["-1"])
   -1.0
   >>> evaluate(["-1.1"])
   -1.1
   >>> evaluate(["2", "1", "+", "3", "*"])
   9.0
   >>> evaluate(["2", "1.9", "+", "3", "*"])
   11.7
   >>> evaluate(["2", "-1.9", "+", "3", "*"])
   0.30000000000000027
   >>> evaluate(["4", "13", "5", "/", "+"])
   6.6
   >>> evaluate(["2", "-", "3", "+"])
   1.0
   >>> evaluate(["-4", "5", "*", "6", "-"])
   -26.0
   >>> evaluate([])
   0
   >>> evaluate(["4", "-", "6", "7", "/", "9", "8"])
   Traceback (most recent call last):
   ...
   ArithmeticError: Input is not a valid postfix expression

   Parameters
   ----------
   post_fix:
       The postfix expression is tokenized into operators and operands and stored
       as a Python list

   verbose:
       Display stack contents while evaluating the expression if verbose is True

   Returns
   -------
   float
       The evaluated value


.. py:function:: parse_token(token: str | float) -> float | str

   Converts the given data to the appropriate number if it is indeed a number, else
   returns the data as it is with a False flag. This function also serves as a check
   of whether the input is a number or not.

   Parameters
   ----------
   token: The data that needs to be converted to the appropriate operator or number.

   Returns
   -------
   float or str
       Returns a float if `token` is a number or a str if `token` is an operator


.. py:data:: OPERATORS

.. py:data:: UNARY_OP_SYMBOLS
   :value: ('-', '+')


.. py:data:: expression