Regexp for python-like function parameters parsing

Question

I am trying to make use questions like this one to devise a regexp that will match and give a function name and all parameters in a very simplified Python-like syntax like the following:

mycall(x, y, hello)

with the desired results:

function name: mycall
parameter 0: x
parameter 1: y
parameter 2: hello

Of course it should also match noparams(), and any number of parameters. As for my simplifications, I just need parameters names, I don't allow default parameters or something different from a list of comma separated names.

My tries with variants of "(\\s*)([A-Za-z0-9_])+\\(\\)" just to match a function name string with spaces at the beginning are failing, with this code:

    std::regex fnregexp(s);

    std::smatch pieces_match;

    if (std::regex_match(q, pieces_match, fnregexp))
    {
        std::cout << ">>>> '" << q << "'" << std::endl;

        for (size_t i = 0; i < pieces_match.size(); ++i)
        {
            std::ssub_match sub_match = pieces_match[i];
            std::string piece = sub_match.str();
            std::cout << "  submatch " << i << ": '" << piece << "'" << std::endl;
        }
    }

I have the following output for " hello()":

>>>> '     hello()'
  submatch 0: '     hello()'
  submatch 1: '     '
  submatch 2: 'o'

With this very basic syntax, is it possible to find name of the function and its parameters?

Cheers!

Not sure what exactly you want to parse: Function declarations like def foo(param): in Python or calls to that function? — besc
– besc, Commented May 19, 2017 at 14:33
A string that matches a Python-like function header, I can also omit def. — senseiwa
– senseiwa, Commented May 19, 2017 at 14:36
No, just one function, nothing fancy for now (for complicated things I'd go with Boost Spirit, probably). — senseiwa
– senseiwa, Commented May 19, 2017 at 14:47
If there is no noise with the function, the simplest regex you could use is \w+. First match would be the function name, each other match would be the arguments — Gawil
– Gawil, Commented May 19, 2017 at 14:55

logi-kal · Accepted Answer · 2017-05-19 15:06:02Z

1

Use this for the conformance check:

^\\s*[A-Za-z_]\\w* *\\( *(?:[A-Za-z_]\\w* *(?:, *[A-Za-z_]\\w* *)*)?\\)$

and if it's ok use this for extracting the parts of signature:

\\w+

the first submatch is the function name, the others are parameters.

EDIT: The correct synthax for Python is [A-Za-z_][A-Za-z0-9_]*

edited May 19, 2017 at 15:06

answered May 19, 2017 at 14:55

logi-kal

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2 Comments

Gawil Over a year ago

You can remove the lookahead, and it will do the same ;) Edit : Oh, you just did ^^

logi-kal Over a year ago

Yes, because originally the answer did not provide the first check, so I thought other kinds of checking were necessary.

besc · Accepted Answer · 2017-05-19 14:54:55Z

1

Matching simple function declarations with regex is feasable. For more complicated things you have exactly the right idea in going with a real parser like Boost Spirit.

The bug in your question is a wrong closing parens in the regex. Compare:

"(\\s*)([A-Za-z0-9_])+\\(\\)" // yours
"(\\s*)([A-Za-z0-9_]+)\\(\\)" // correct

The capture group in your version captures only a single character. Because of how the regex engine works it is the last one matched: the o. The correct version includes the + in the group and captures hello as expected.

answered May 19, 2017 at 14:54

besc

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