34 lines
973 B
Python
34 lines
973 B
Python
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"""Parse arbitrary math equations in a safe way.
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Gratefully copied from https://stackoverflow.com/a/9558001
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"""
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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 = {ast.Add: op.add, ast.Sub: op.sub, ast.Mult: op.mul, ast.Div: op.truediv, ast.Pow: op.pow, ast.BitXor: op.xor, ast.USub: op.neg}
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def compute(expr):
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"""Parse a mathematical expression and return the answer.
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>>> compute('2^6')
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4
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>>> compute('2**6')
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64
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>>> compute('1 + 2*3**(4^5) / (6 + -7)')
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-5.0
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"""
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return _eval(ast.parse(expr, mode='eval').body)
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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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