[Python-ideas] New list methods

[Steven D'Aprano]

On Wed, 6 May 2009 06:20:31 am Carl Johnson wrote:
> Would there be any interest in adding a 'reversed' kwarg to the
> relevant string methods, deprecating the r-methods in Python 3.2, and
> removing them in Python 3.3? It might make things a little simpler
> and unclutter the dir for strings a bit…


-0.5 from me. I think a "reversed" argument clutters up the signature of 
the various find() methods (etc) for little or no benefit, and 
certainly not enough benefit to make up for the hassle of going through 
the depreciation process and breaking compatibility with existing code.

A "reversed" kwarg would only be useful when you don't know which 
direction you want to search in until runtime. How often does that 
happen? In practice, I believe you will nearly always know whether you 
want to search from the left or the right when you're writing the code. 
so I expect the "reversed" kwarg will nearly always be given as a 
constant:

astring.find("spam", reversed=True)

as opposed to:

astring.find("spam", reversed=(today==Wednesday))

A slightly whimsical example, but I hope it illustrates the point.

On the rare occasion that you do need a flag to distinguish "operate 
from the left" from "operate from the right", I don't believe it is a 
hardship to use something like the following idiom:

def func(astring, arg, ... , reversed=False):
    if reversed:  find = astring.find
    else:  find = astring.rfind
    ...
    n = find(arg)



-- 
Steven D'Aprano