how to convert string function to string method?

[Dr. Phillip M. Feldman]

I wrote a handy-dandy function (see below) called "strip_pairs" for stripping
matching pairs of characters from the beginning and end of a string.  This
function works, but I would like to be able to invoke it as a string method
rather than as a function.  Is this possible?

def strip_pairs(s=None, open='([{\'"', close=')]}\'"'):
   """This function strips matching pairs of characters from the beginning
and
   end of the input string `s`.  `open` and `close` specify corresponding
pairs
   of characters, and must be equal-length strings.  If `s` begins with a
   character in `open` and ends with the corresponding character in `close`,
   both are removed from the string.  This process continues until no
further
   matching pairs can be removed."""

   if len(open) != len(close): raise Exception, \
     '\'open\' and \'close\' arguments must be strings of equal length.'

   # If input is missing or is not of type `str` (or `unicode`), return
None:
   if s is None or not isinstance(s,(str,unicode)): return None

   while len(s) >= 2:

      # Check whether first character of `s` is in `open`:
      i= open.find(s[0])

      # If `s` does not begin with a character from `open`, there are no
more
      # pairs to be stripped:
      if i == -1: break

      # If `s` does not begin and end with matching characters, there are no
      # more pairs to be stripped:
      if s[-1] != close[i]: break

      # Strip the first and last character from `s`:
      s= s[1:-1]

   return s
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