Python: extract substitution vars from format string

Python: extract substitution vars from format string

I have to 'parse' a format string in order to extract the variables.
E.g.
>>> s = "%(code)s - %(description)s"
>>> get_vars(s)
'code', 'description'
I managed to do that by using regular expressions:
re.findall(r"%\((\w+)\)", s)
but I wonder whether there are built-in solutions (actually Python do
parse the string in order to evaluate it!).