Source code for at.load.rpn
"""RPN interpreter. From Onel Harrison:
https://onelharrison.medium.com/watch-building-a-reverse-polish-notation-rpn-evaluator-in-python-75b1c910fab6.
"""
from __future__ import annotations
__all__ = ["Rpn"]
import operator as op
from math import sqrt, sin, cos, pi, pow
from typing import Any
Number = int | float | str
# noinspection PyUnusedLocal
def _pop(x):
return []
def _swap(x, y):
return [y, x]
supported_operators = {
"+": (op.add, 2),
"-": (op.sub, 2),
"*": (op.mul, 2),
"/": (op.truediv, 2),
"sqrt": (sqrt, 1),
"pi": (pi, 0),
"sin": (sin, 1),
"cos": (cos, 1),
"pow": (pow, 2),
"pop": (_pop, 1),
"swap": (_swap, 2),
}
[docs]
class Rpn:
def __init__(self):
self.stack = []
self.store = False
self.operators = supported_operators.copy()
def _mpop(self, n: int = 1) -> list[Any]:
"""Pops and returns `n` items from the stack."""
try:
return [self.stack.pop() for _ in range(n)]
except IndexError:
msg = "RPN: Malformed expression: empty stack"
raise SyntaxError(msg) from None
@staticmethod
def _to_num(x: Any) -> Number:
"""Converts a value to its appropriate numeric type."""
try:
n = float(x)
except ValueError:
return x
else:
return int(n) if n.is_integer() else n
def _consume_token(self, token: str) -> None:
"""Consumes a token given the current stack and returns the updated stack."""
if token == "sto":
self.store = True
return
elif self.store:
self.operators[token] = (self.stack[-1], 0)
self.store = False
return
try:
oper, narg = self.operators[token]
except KeyError:
result = self._to_num(token)
else:
result = oper if narg == 0 else oper(*reversed(self._mpop(narg)))
if isinstance(result, list):
self.stack.extend(result)
else:
self.stack.append(result)
[docs]
def evaluate(self, expr: str) -> Number:
"""Evaluate an RPN expression and return the result."""
for token in expr.split():
self._consume_token(token)
(result,) = self._mpop(1)
if self.stack:
msg = "RPN: Found extra tokens"
raise SyntaxError(msg)
return result
