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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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