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- """Parse arbitrary math equations in a safe way.
-
- Gratefully copied from https://stackoverflow.com/a/9558001
- """
- import ast
- import operator as op
-
- # supported operators
- 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}
-
-
- def compute(expr):
- """Parse a mathematical expression and return the answer.
-
- >>> compute('2^6')
- 4
- >>> compute('2**6')
- 64
- >>> compute('1 + 2*3**(4^5) / (6 + -7)')
- -5.0
- """
- return _eval(ast.parse(expr, mode='eval').body)
-
-
- def _eval(node):
- if isinstance(node, ast.Num): # <number>
- return node.n
- elif isinstance(node, ast.BinOp): # <left> <operator> <right>
- return operators[type(node.op)](_eval(node.left), _eval(node.right))
- elif isinstance(node, ast.UnaryOp): # <operator> <operand> e.g., -1
- return operators[type(node.op)](_eval(node.operand))
- else:
- raise TypeError(node)
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