Regular expression to match function name and all arguments in Python

Question

Suppose I have a string such as the following:

"func(arg1, arg2, arg3, arg4, ..., argn)"

EDIT: This function is not in some particular language. It just has this format. If it makes it easier, don't think of it as a function call, just a string.

I want to write a regular expression to match the function and each of the arguments. I am writing this in Python. The desired output of this is:

{"function" : "func", "arg" : ["arg1", "arg2", ... , "argn"]}

EDIT: While the arguments could be function calls, I can easily recursively try to match them with the same regular expression once I create one that works. By this I mean I can recurse on the function with each of the arguments. But this is not really relevant. I am not trying to create an interpreter, just something to recognize the arguments.

Here is my attempt at this:

import re
s = "func(arg1, arg2, arg3, arg4, argn)"
m = re.match(r"(?P<function>\w+)\s?\((?P<args>(?P<arg>\w+(,\s?)?)+)\)", s)
print m.groupdict()

And here is the output:

{'function': 'func', 'args': 'arg1, arg2, arg3, arg4, argn', 'arg': 'argn'}

The function matches just fine, and so does the argument set. However, I can't seem to match the individual arguments. Is this a problem with my regex, or a limitation of Python regular expression matching?

EDIT2: I am aware that I can now split the arguments using the following code:

d["arg"] = d["args"].split(", ")

But I was wondering if I could do the whole job with regular expressions. In particular, I am wondering why "arg" is matched to only the last argument.

EDIT3: I guess I am (1) hoping to figure out why Python only matches the last argument every time, and (2) whether I can do Scheme-style pattern-matching in Python. Or if there is something just as intuitive in Python as Scheme-style pattern matching. I looked at the ast module, and its syntax is prohibitively complex.

Answer 1

Regular expressions cannot parse complex programming languages.

If you're just trying to parse Python, I suggest taking a look at the ast module, which will parse it for you.

Answer 2

Looks like you're 90% there, why not just swap the arg and args groupings and do:

import re

fn_match = re.match(r"(?P<function>\w+)\s?\((?P<arg>(?P<args>\w+(,\s?)?)+)\)", s)
fn_dict = fn_match.groupdict()
del fn_dict['args']
fn_dict['arg'] = [arg.strip() for arg in fn_dict['arg'].split(',')]