data_structures.stacks.postfix_evaluation

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

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

OPERATORS

UNARY_OP_SYMBOLS

expression

Functions

evaluate(→ float)

Evaluate postfix expression using a stack.

parse_token(→ float | str)

Converts the given data to the appropriate number if it is indeed a number, else

Module Contents

data_structures.stacks.postfix_evaluation.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

data_structures.stacks.postfix_evaluation.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

data_structures.stacks.postfix_evaluation.OPERATORS
data_structures.stacks.postfix_evaluation.UNARY_OP_SYMBOLS = ('-', '+')
data_structures.stacks.postfix_evaluation.expression