Dr. Phillip M. Feldman wrote:
> 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
I've never tried it but I think it is possible to inject new methods
into existing classes, see...
http://www.daniel-lemire.com/blog/archives/2005/12/21/metaclass-programming-in-python/
Not sure how good an idea it would be though, I have heard it refered to
as "monkey patching" and I can imagine doing it to classes as
fundamental as the string class could have negative performace consequences.
Roger.
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