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I googled little around for correct way to not reinventing of the wheel for expression evaluation (even I had done some simple evaluation check for my [Tkinter calculator snippet](http://www.daniweb.com/software-development/python/code/282548/simple-calculator) earlier). After getting totally upset with [this example](http://www.bestcode.com/html/evaluate_math_expressions_pyth.html), I made this with some struggles with `__builtins__` globals parameter of eval. First …