Dr. Phillip M. Feldman a écrit :
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?
No. Basic type (strings/unicode, numerics, lists, tuples, dicts etc) are
not "opened" to monkeypatching. Partly for performance reasons, partly
to avoid the insanity that we've seen in the Ruby world where everyone
and it's little sisters extends basic types with tons of more or less
usefull and often conflicting features.
def strip_pairs(s=None, open='([{\'"', close=')]}\'"'):
Why a default value of None for the first param ???
"""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.'
Please use proper exception types. Here you want a ValueError. Also, you
just dont care whether open and close are proper strings - any sequence
of characters would do.
# 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
If s is None, it won't be a str or unicode instance, so the test is
redundant !-)
But anyway : if this function is supposed to operate on strings, don't
accept None (and even less provide it as default), and don't fail
silently - you should really raise a TypeError here IMHO.
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
HTH
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