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comp / comp.lang.python / Re: Two python issues

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o Re: Two python issuesRoel Schroeven

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Subject: Re: Two python issues
From: Roel Schroeven
Newsgroups: comp.lang.python
Date: Wed, 6 Nov 2024 09:36 UTC
References: 1 2
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From: roel@roelschroeven.net (Roel Schroeven)
Newsgroups: comp.lang.python
Subject: Re: Two python issues
Date: Wed, 6 Nov 2024 10:36:01 +0100
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View all headers

Op 5/11/2024 om 15:48 schreef Raymond Boute via Python-list:
> L.S.,
>
> Python seem to suffer from a few poor design decisions regarding
> strings and lists that affect the elegance of the language.
>
> (a) An error-prone "feature" is returning -1 if a substring is not
> found by "find", since -1 currently refers to the last item. An example:
This is IMO indeed not the best design decision. Fortunately there's an
alternative: the "index" method on strings, which raises exception
ValueError when the substring is not found, instead of returning -1. An
example:

>>> s = 'qwertyuiop'
>>> s[s.index('p')]
'p'
>>> s[s.index('a')]
Traceback (most recent call last):
  File "<pyshell#3>", line 1, in <module>
    s[s.index('a')]
ValueError: substring not found

> Moreover, using index -1 for the last item is a bad choice: it should
> be len(s) - 1 (no laziness!).
> Negative indices should be reserved for elements preceding the element
> with index 0 (currently not implemented, but a must for orthogonal
> design supporting general sequences).
I don't agree, I think this is a case of "practicality beats purity".
Being able to use negative indices to index from the end is often very
useful in my experience, and leads to code that is much easier to grok.
General sequences on the other hand is a concept that I don't see ever
implemented in Python (or most other programming languages AFAIK). I
think it would be wrong to avoid implementing a feature that's very
useful in practice in order to keep the door open for a theoretical
feature that's probably not even wanted in the language.
> (b) When using assignment for slices, only lists with the same length
> as the slice should be acceptable, otherwise an error should be
> given.  Anything that re-indexes items not covered by the slice is
> against the essential idea of assignment. For changes that imply
> re-indexing (e.g., inserting a list longer than the slice), Python
> offers cleaner solutions.
Again I don't agree. I don't see anything wrong with replacing a part of
a list with something that's longer, or shorter, or even empty. It's
very practical, and I don't see how it's against the essential idea of
assignment (or actually I'm not even sure what you mean by that).

Two closing remarks:

(1) I think that Python indeed has some warts, inconsistencies, gotchas.
I think this is unavoidable in any complex system. Python got rid of a
number of those in the transition from Python 2 to Python 3; others
might remain forever. Overall though I feel Python is more consistent
than most other programming languages I come in contact with.

(2) Design decisions are not necessarily wrong when they don't match
your mental model, or don't match what you know from other languages.
Often there are different valid options, each with their own tradeoffs.

--
"Programming today is a race between software engineers striving to build bigger
and better idiot-proof programs, and the Universe trying to produce bigger and
better idiots. So far, the Universe is winning."
-- Douglas Adams

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