62 lines
1.7 KiB
Python
62 lines
1.7 KiB
Python
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# calculator.py
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class Calculator:
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def __init__(self):
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self.operators = {
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"+": lambda a, b: a + b,
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"-": lambda a, b: a - b,
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"*": lambda a, b: a * b,
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"/": lambda a, b: a / b,
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}
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self.precedence = {
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"+": 1,
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"-": 1,
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"*": 2,
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"/": 2,
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}
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def evaluate(self, expression):
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if not expression or expression.isspace():
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return None
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tokens = expression.strip().split()
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return self._evaluate_infix(tokens)
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def _evaluate_infix(self, tokens):
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values = []
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operators = []
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for token in tokens:
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if token in self.operators:
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while (
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operators
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and operators[-1] in self.operators
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and self.precedence[operators[-1]] >= self.precedence[token]
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):
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self._apply_operator(operators, values)
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operators.append(token)
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else:
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try:
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values.append(float(token))
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except ValueError:
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raise ValueError(f"invalid token: {token}")
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while operators:
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self._apply_operator(operators, values)
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if len(values) != 1:
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raise ValueError("invalid expression")
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return values[0]
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def _apply_operator(self, operators, values):
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if not operators:
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return
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operator = operators.pop()
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if len(values) < 2:
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raise ValueError(f"not enough operands for operator {operator}")
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b = values.pop()
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a = values.pop()
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values.append(self.operators[operator](a, b))
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