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Asked: 2026-06-02T07:11:01+00:00

If I have: statement = (2*(3+1))*2 I want to be able to handle multiple

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If I have:

statement = "(2*(3+1))*2"

I want to be able to handle multiple parentheses within parentheses for a math reader I’m writing. Perhaps I’m going about this the wrong way, but my goal was to recursively go deeper into the parentheses until there were none, and then I would perform the math operations. Thus, I would first want to focus on 

"(2*(3+1))"

then focus on 

"(3+1)"

I hoped to do this by assigning the focus value to the start index of the regex and the end index of the regex. I have yet to figure out how to find the end index, but I’m more interested in first matching the regex

r"\(.+\)"

failed to match. I wanted it to read as “any one or more characters contained within a set of parentheses”. Could someone explain why the above expression will not match to the above statement in python?

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1 Answer

  1. Editorial Team

    I love regular expressions. I use them all the time.

    Don’t use regular expressions for this.

    You want an actual parser that will actually parse your math expressions. You might want to read this:

    http://effbot.org/zone/simple-top-down-parsing.htm

    Once you have actually parsed the expression, it’s trivial to walk the parse tree and compute the result.

    EDIT: @Lattyware suggested pyparsing, which should also be a good way to go, and might be easier than the EFFBot solution posted above.

    https://github.com/pyparsing/pyparsing

    Here’s a direct link to the pyparsing sample code for a four-function algebraic expression evaluator:

    http://pyparsing.wikispaces.com/file/view/fourFn.py

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