PEP 358 and operations on bytes

Steve Holden steve at
Wed Oct 4 04:28:04 CEST 2006

Ben Finney wrote:
> Gabriel G <gabrielg_laburando at> writes:
>>At Tuesday 3/10/2006 21:52, Ben Finney wrote:
>>>Gerrit Holl <gerrit at> writes:
>>>>    - str methods endswith, find, partition, replace, split(lines),
>>>>      startswith,
>>>>    - Regular expressions
>>>Looking at those, I don't see why they wouldn't be useful for *all*
>>>sequence types. Perhaps there needs to be a 'seq' type containing
>>>those common methods, that is the superclass of 'str', 'bytes',
>>>'list', 'tuple' et cetera.
>>find() could be useful sometimes.
>>But what means partition, replace, split, etc on a generic sequence?
>     >>> "spamandeggs".partition("and")
>     ('spam', 'and', 'eggs')
>     >>> ["foo", "bar", "spam", "baz", "quux", "wibble"].partition("spam")
>     (["foo", "bar"], ["spam"], ["baz", "quux", "wibble"])
>     >>> "spamandeggs".startswith("spam")
>     True
>     >>> ["foo", "bar", "spam", "baz", "quux", "wibble"].startswith("foo")
>     True
> i.e. the 'str' methods can be seen as operating on a sequence of
> characters; their 'str' return values are likewise sequences of
> characters. That can be generalised to a sequence of the same type as
> the instance; so, in the examples above, the 'list' methods operate on
> sub-lists.
> Perhaps not all of the mentioned methods make sense for all sequence
> types. But I think it would be useful to have a common set of
> functionality available for all sequence types, in a common ancestor.
This would just be bloat without any use cases being demonstrated. What 
is your crying need for these methods? The second one, by the way, is 
normally spelled:

     ["foo", "bar", "spam", "baz", "quux", "wibble"][0] == "foo"

Your *real* generalisation of the string method would actually require 
you to write

     ["foo", "bar", "spam", "baz", "quux", "wibble"].startswith(["foo"])

because you also need to be able to write

     ["foo", "bar", "spam", "baz", "quux", "wibble"].\
                                 startswith(["foo", "bar"])

OK, a startswith() method could return false on a zero-length sequence 
to avoid having to program around that corner case, but I question the 
need for this. Similarly your first example would need to take a list 

Python didn't get to be the language it is today by adding  unnecessary 
hypergeneralisations on a whim. Show me how these methods will improve 
the daily lives of programmers and I'll champion them to the developers, 
but I don't think the world will be beating a path to your door.

Steve Holden       +44 150 684 7255  +1 800 494 3119
Holden Web LLC/Ltd
Skype: holdenweb
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