extracting keywords from %(keyword)s-based templates

[Thomas Weholt]

Sorry for that stupid subject, but ...

Take this piece of code :

def parse(s):
    keywords = []
    dict = {}
    while 1:
        try:
            str(s % dict)
            break
        except KeyError, e:
            keywords.append(str(e))
            dict[str(e)] = ''
        except:
            raise "Bad format-chars in input-string. Use
'%(keyword)s'-format only." # things like %d etc. not supported. Tips
wanted!!!
    return keywords

if __name__ == '__main__':
    # define a template s :
    s = """
    Hello %(somebody)s,

    How's the weather in %(someplace)s?

    Best regards,
    %(me)s
    """
    print parse(s)

# output is
['somebody', 'someplace', 'me']

The object is to extract all keywords used in a template. Is there a quicker
way, possibly using regular expressions?
This also just traps %(keyword)s-format. How do I trap stuff like %d etc. ??

Thomas