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How to Evaluate RPN Expressions in Python

Use a stack to evaluate Reverse Polish Notation token lists with a dictionary of operator lambdas, truncating division toward zero.

rpn stack expression

Python

def eval_rpn(tokens):
    stack = []
    ops = {
        '+': lambda a, b: a + b,
        '-': lambda a, b: a - b,
        '*': lambda a, b: a * b,
        '/': lambda a, b: int(a / b)  # truncate toward zero
    }
    for token in tokens:
        if token in ops:
            b = stack.pop()
            a = stack.pop(…

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