math_ops.py (982B)
1 """Parse arbitrary math equations in a safe way. 2 3 Gratefully copied from https://stackoverflow.com/a/9558001 4 """ 5 import ast 6 import operator as op 7 8 # supported operators 9 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} 10 11 12 def compute(expr): 13 """Parse a mathematical expression and return the answer. 14 15 >>> compute('2^6') 16 4 17 >>> compute('2**6') 18 64 19 >>> compute('1 + 2*3**(4^5) / (6 + -7)') 20 -5.0 21 """ 22 return _eval(ast.parse(expr, mode='eval').body) 23 24 25 def _eval(node): 26 if isinstance(node, ast.Constant): # <number> 27 return node.value 28 elif isinstance(node, ast.BinOp): # <left> <operator> <right> 29 return operators[type(node.op)](_eval(node.left), _eval(node.right)) 30 elif isinstance(node, ast.UnaryOp): # <operator> <operand> e.g., -1 31 return operators[type(node.op)](_eval(node.operand)) 32 else: 33 raise TypeError(node)