Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!feeder.news-service.com!newsfeed.xs4all.nl!newsfeed6.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
From: Lee Harr <missive@hotmail.com>
To: <python-list@python.org>
Subject: parsing function parameters
Date: Wed, 3 Aug 2011 20:32:04 +0430
Importance: Normal
Content-Type: text/plain; charset="windows-1256"
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.1843.1312387394.1164.python-list@python.org>
Lines: 66
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:10811


I am trying to get some information about a function
before (and without) calling it.

Here is what I have so far. I chose to go with a
regular expression, so now I have 2 problems :o)



def pdict(f, pstr):
    '''given a function object and a string with the function parameters,
    return a dictionary of {parameter name: default value or None, ...}


    I don't really need the actual default values, just knowing that
    they exist or having their string representations would be fine.


    def foo(x, y, z=50):
        pass

    ps = 'x, y, z=50'

    pdict(foo, ps)
    {'x': None, 'y': None, 'z': 50}
    OR: {'x': '', 'y': '', 'z': '50'}
    OR: {'x': False, 'y': False, 'z': True}


    Note that the parameter list can be arbitrarily complex
        (as long as it is legal python)

    def bar(m, n=(1, 2, 3), o  =  ('n=5', 'or anything legal')):
        pass

    pps = 'm, n=(1, 2, 3), o  =  ('n=5', 'or anything legal')'

    pdict(bar, pps)
    {'m': None, 'n': '(1, 2, 3)', 'o': "('n=5', 'or anything legal')"}

    '''
    prs = f.func_code.co_varnames
    rxl = [r'(\s*%s\s*=(?=(?:\s*\S+))\s*\S+)\s*'%pr for pr in prs]
    rx = ','.join(rxl)
    print rx


    import re
    re.match(rx, pstr).groups()


This regex works in limited situations, namely when every parameter
has a default value, but I can't figure out how to also make it
match a parameter that has no default.


I am open to any solution, though I am reluctant to pull in any more
external libraries just for this one little enhancement. I have it
working by just splitting the pstr on comma, except of course that
it fails when the default value contains a comma (a tuple or list,
for instance).


Any assistance or ideas appreciated.