41 lines
1.2 KiB
Python
41 lines
1.2 KiB
Python
"""AST evaluator for calc expressions.
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evaluate(node) -> int | float
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Result-type rule:
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- Whole-valued results (including float 2.0) are returned/displayed as int.
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- Non-whole results are returned as float.
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Division by zero raises EvalError, not a bare ZeroDivisionError.
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"""
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from calc.parser import Num, BinOp, Unary, Node
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class EvalError(Exception):
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pass
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def evaluate(node: Node) -> "int | float":
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if isinstance(node, Num):
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return node.value
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if isinstance(node, Unary):
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if node.op == "-":
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return -evaluate(node.operand)
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raise EvalError(f"unknown unary op {node.op!r}")
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if isinstance(node, BinOp):
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left = evaluate(node.left)
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right = evaluate(node.right)
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if node.op == "+":
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return left + right
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if node.op == "-":
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return left - right
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if node.op == "*":
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return left * right
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if node.op == "/":
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if right == 0:
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raise EvalError("division by zero")
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result = left / right
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return int(result) if result == int(result) else result
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raise EvalError(f"unknown binary op {node.op!r}")
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raise EvalError(f"unknown node type {type(node).__name__}")
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