Re^3: Converting python list range expressions to perl

"Ken, thanks for your writeup, including forcing me to learn a bit about Test -- I needed that! :-)"

You're welcome. It's good to be able to start a script with use v5.36;.

"I'd rather stick with Perl's slice capability since it reads more cleanly (to me, anyway) ..."

What you choose is entirely up to you. This correlation stood out for me:

Python	Perl
`[OFFSET:LENGTH]`	`splice ARRAY, OFFSET, LENGTH`
`[:LENGTH]`	`splice ARRAY, 0, LENGTH`
`[OFFSET:]`	`splice ARRAY, OFFSET`
`[:]`	`splice ARRAY, 0`

"... and doesn't require copying and modifying the source array."

The source array, @test_array, is not modified at all. The temporary copy, @temp_array, is modified in the last statement of (my) get_array_slice_by_python_expr() function; it's then immediately discarded as it goes out of scope.

I added your three new tests, plus a fourth ([:]), to my original code:

    [\@test_array, '[-3:-1]', 'ef'],
    [\@test_array, '[-3:-3]', ''],
    [\@test_array, '[3:-1]',  'def'],
    [\@test_array, '[:]',  'abcdefg'],
[download]

All pass:

1..8
ok 1 - Testing: [:3]
ok 2 - Testing: [:-3]
ok 3 - Testing: [3:]
ok 4 - Testing: [-3:]
ok 5 - Testing: [-3:-1]
ok 6 - Testing: [-3:-3]
ok 7 - Testing: [3:-1]
ok 8 - Testing: [:]
[download]

— Ken

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Re^4: Converting python list range expressions to perl by ibm1620 (Hermit) on Dec 04, 2022 at 23:22 UTC
I didn't mean that `@test_array` was modified; I meant that `splice()` modifies its argument array, requiring a temp copy be made. It just seemed wasteful to copy an array, and modify it, and then dispose of it, when Perl slice doesn't do so. Of course, that's pure guesswork on my part - and I haven't attempted to time it. In your representation of Python vs Perl slicing & splicing, I didn't understand your notation OFFSET:LENGTH for Python. Python slices are OFFSET:OFFSET. (Which is why Perl slices seemed a better fit to me.) Could you clarify?	[reply] [d/l] [select]
Re^5: Converting python list range expressions to perl by kcott (Archbishop) on Dec 05, 2022 at 06:14 UTC
`OFFSET:LENGTH` vs. `OFFSET:OFFSET` may be purely semantics. The relationship that I showed in the table is exactly the way I coded it in my script. Can you come up with any new tests which aren't successful? — Ken	[reply] [d/l] [select]
Re^6: Converting python list range expressions to perl by LanX (Saint) on Dec 05, 2022 at 14:23 UTC
> OFFSET:LENGTH vs. OFFSET:OFFSET may be purely semantics. doesn't seem so. https://docs.python.org/3/glossary.html#term-slice `slice An object usually containing a portion of a sequence. A slice is creat +ed using the subscript notation, [] with colons between numbers when several are given, such as in variable_nam +e[1:3:5]. The bracket (subscript) notation uses slice objects internally.` [download] https://docs.python.org/3/library/functions.html#slice `class slice(stop) class slice(start, stop, step=1) Return a slice object representing the set of indices specified by ran +ge(start, stop, step). The start and step arguments default to None. ...` [download] something is off (-set ;) with this test suite. Unfortunately I have no Python at hand to test ... updates references and citations updated Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^7: Converting python list range expressions to perl by kcott (Archbishop) on Dec 05, 2022 at 19:02 UTC
Re^8: Converting python list range expressions to perl by LanX (Saint) on Dec 05, 2022 at 20:15 UTC
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Re^6: Converting python list range expressions to perl by ibm1620 (Hermit) on Dec 05, 2022 at 21:36 UTC
Here's one: `[\@test_array, '[3:4]', 'd'],` [download] In my OP I mentioned needing help from "bilingual" (i.e. Perl and Python) people; otherwise I'd have included a description of Python's slice notation. I'm sorry if this was negligence on my part, but I assumed that anyone answering would be familiar with Python's oddball slice semantics. `[a:b]` means "the characters starting at offset a and ending at offset b-1". Unless a or b is negative in which case .. hell, I don't remember ;-) The code I posted correctly slices arrays using Pythonic parameters, although it doesn't attempt to handle the optional third argument, a step value. And I'm happy to say that the translation effort has succeeded and Perl is now churning out gibberish sonnets at a much faster rate than its Python equivalent. Update: It correctly slices arrays if the arguments aren't nonsensical -- like being out of range, which Python forgives. It needs a few more sanity tests to handle those cases.	[reply] [d/l] [select]
Re^7: Converting python list range expressions to perl by LanX (Saint) on Dec 05, 2022 at 22:11 UTC
Re^8: Converting python list range expressions to perl by ibm1620 (Hermit) on Dec 05, 2022 at 22:58 UTC


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Re^3: Converting python list range expressions to perl

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