45 lines
1.1 KiB
Python
45 lines
1.1 KiB
Python
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# Adapted from https://stackoverflow.com/a/9558001/2536294
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import ast
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import operator as op
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# supported operators
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operators = {
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ast.Add: op.add,
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ast.Sub: op.sub,
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ast.Mult: op.mul,
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ast.Div: op.truediv,
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ast.FloorDiv: op.floordiv,
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ast.Mod: op.mod,
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ast.Pow: op.pow,
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ast.USub: op.neg,
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}
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def eval_expr(expr):
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"""
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>>> eval_expr('2*6')
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12
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>>> eval_expr('2**6')
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64
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>>> eval_expr('1 + 2*3**(4) / (6 + -7)')
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-161.0
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"""
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try:
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return eval_(ast.parse(expr, mode="eval").body)
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except (TypeError, SyntaxError, KeyError) as e:
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raise ValueError(
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f"{expr!r} is not a valid or supported arithmetic expression."
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) from e
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def eval_(node):
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if isinstance(node, ast.Num): # <number>
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return node.n
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elif isinstance(node, ast.BinOp): # <left> <operator> <right>
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return operators[type(node.op)](eval_(node.left), eval_(node.right))
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elif isinstance(node, ast.UnaryOp): # <operator> <operand> e.g., -1
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return operators[type(node.op)](eval_(node.operand))
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else:
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raise TypeError(node)
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