python - Math Expression Evaluation

Question

What is the best way to implement a python program that will take a string and will output its result according to operator precedence (for example: "4+3*5" will output 19). I've googled for ways to solve this problem but they were all too complex, and I'm looking for a (relatively) simple one.

clarification: I need something slightly more advanced than eval() - I want to be able to add other operators (for example a maximum operator - 4$2 = 4) or, also I am more interested in this academically than professionaly - I want to know how to do this.

Answer 1

If you're "academically interested", you want to learn about how to write a parser with operator precedence.

Simple Top-Down Parsing in Python is a nice article that builds an example parser to do exactly what you want to do: Evaluate mathematical expressions.

I can highly recommend having a go at writing your own first parser -- it's one of those "ah, that's how that works" moments!