Cutting slices

[MRAB]

On 2023-03-06 00:28, dn via Python-list wrote:
> On 06/03/2023 11.59, aapost wrote:
>> On 3/5/23 17:43, Stefan Ram wrote:
>>>    The following behaviour of Python strikes me as being a bit
>>>    "irregular". A user tries to chop of sections from a string,
>>>    but does not use "split" because the separator might become
>>>    more complicated so that a regular expression will be required
>>>    to find it. But for now, let's use a simple "find":
>>> |>>> s = 'alpha.beta.gamma'
>>> |>>> s[ 0: s.find( '.', 0 )]
>>> |'alpha'
>>> |>>> s[ 6: s.find( '.', 6 )]
>>> |'beta'
>>> |>>> s[ 11: s.find( '.', 11 )]
>>> |'gamm'
>>> |>>>
>>>
>>>    . The user always inserted the position of the previous find plus
>>>    one to start the next "find", so he uses "0", "6", and "11".
>>>    But the "a" is missing from the final "gamma"!
>>>    And it seems that there is no numerical value at all that
>>>    one can use for "n" in "string[ 0: n ]" to get the whole
>>>    string, isn't it?
>>>
>>>
>> 
>> I would agree with 1st part of the comment.
>> 
>> Just noting that string[11:], string[11:None], as well as string[11:16] 
>> work ... as well as string[11:324242]... lol..
> 
> To expand on the above, answering the OP's second question: the numeric
> value is len( s ).
> 
> If the repetitive process is required, try a loop like:
> 
>   >>> start_index = 11	#to cure the issue-raised
> 
>   >>> try:
> ...     s[ start_index:s.index( '.', start_index ) ]
> ... except ValueError:
> ...     s[ start_index:len( s ) ]
> ...
> 'gamma'
> 
Somewhat off-topic, but...

When there was a discussion about a None-coalescing operator, I thought 
that it would've been nice if .find and .rfind returned None instead of -1.

There have been times when I've wanted to find the next space (or 
whatever) and have it return the length of the string if absent. That 
could've been accomplished with:

     s.find(' ', pos) ?? len(s)

Other times I've wanted it to return -1. That could've been accomplished 
with:

     s.find(' ', pos) ?? -1

(There's a place in the re module where .rfind returning -1 is just the 
right value.)

In this instance, slicing with None as the end is just what's wanted.

Ah, well...