#!/usr/bin/env python3

__author__ = ['J. Sebastian', '[Brandon Amos](http://bamos.github.io)']

__date__ = '2013.08.01'

"""

A module to evaluate a mathematical expression using Python's AST.

+ Original by: J. Sebastian at http://stackoverflow.com/questions/2371436.

+ Modifications by: [Brandon Amos](http://bamos.github.io).

If you want a command-line expression evaluator, use

[Russell91/pythonpy](https://github.com/Russell91/pythonpy).

```

$ eval-expr.py '(((4+6)*10)<<2)'

(((4+6)*10)<<2) = 400

```

"""

import ast

import operator as op

class EvalExpr:

def __init__(self, varMap):

self.ops = {ast.Add: op.add, ast.Sub: op.sub, ast.Mult: op.mul,

ast.Div: op.truediv, ast.Mod: op.mod, ast.Pow: op.pow,

ast.LShift: op.lshift, ast.RShift: op.rshift,

ast.BitOr: op.or_, ast.BitXor: op.xor, ast.BitAnd: op.and_,

ast.FloorDiv: op.floordiv, ast.Invert: op.invert,

ast.Not: op.not_, ast.UAdd: op.pos, ast.USub: op.neg}

self.varMap = varMap

def evalExpr(self, expr):

return self.__eval(ast.parse(expr).body[0].value)

def __eval(self, node):

if isinstance(node, ast.Num):

return node.n

elif type(node) in self.ops:

return self.ops[type(node)]

elif isinstance(node, ast.UnaryOp):

return self.__eval(node.op)(self.__eval(node.operand))

elif isinstance(node, ast.BinOp):

return self.__eval(node.op)(self.__eval(node.left),

self.__eval(node.right))

elif node.id in self.varMap:

return self.varMap[node.id]

else:

raise TypeError(node)

if __name__ == "__main__":

import sys

if len(sys.argv) == 2:

expr = sys.argv[1]

print(expr + " = " + str(EvalExpr({}).evalExpr(expr)))

else:

print("Usage: ./EvalExpr.py <mathematical expression>")