[Python-ideas] str.rreplace

[Andrew Barnert]

From: Ron Adam <ron3200 at gmail.com>

Sent: Monday, January 27, 2014 7:18 PM


> On 01/24/2014 07:36 PM, Andrew Barnert wrote:
>>  I was responding to Serhiy's (probably facetious or devil's advocate)
>>  suggestion that we should regularize the API: add rfind and rindex to
>>  tuple (and presumably Sequence), and those plus rremove to list (and
>>  presumably MutableSequence), and so on.
>> 
>>  My point was that if we're going to be that radical, we might as well
>>  consider removing methods instead of adding them. Some of the find-like
>>  methods already take negative indices; expanding that to all of the
>>  index-based methods, and doing the equivalent to the count-based ones,
>>  and adding a count or index to those that have neither, would mean all
>>  of the "r" variants could go away.
> 
> How about a keyword to specify which end to index from?  When used, it would 
> disable negative indexing as well.  When not used the current behaviour with 
> negative indexing would be the default.
> 

>     direction=0            # The default with the current
>     (or not specified)     #    negative indexing allowed.
> 
>     direction=1   # From first. Negative indexing disallowed.
>     direction=-1  # From last.  Negative indexing disallowed.
> 

> (A shorter key word would be nice, but I can't think of any that is as 
> clear.)

Why does it have to be -1/0/1 instead of just True/False?

In which case we could use "reverse", the same name that's already used for similar things in other methods like list.sort (and that's implied in the current names "rfind", etc.).

> The reason for turning off the negative indexing is it would also offer a way to 

> avoid some indexing bugs as well.  (Using negative indexing with a reversed 
> index is just asking for trouble I think.)

But str.rfind takes negative indices today:

    >>> 'abccba'.rfind('b', -5, -3)
    1

Why take away functionality that already works?

And of course str.find takes negative indices and that's actually used in some quick&dirty scripts:

    >>> has_ext = path.find('.', -4)

Of course you could make an argument that any such scripts deserve to be broken…