[issue41324] Add a minimal decimal capsule API

[Daniele Varrazzo]

Daniele Varrazzo  added the comment:

Ah, just noticed that this has been now reverted. Oh well, I'll see what to do 
then :(

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[issue41324] Add a minimal decimal capsule API

[Daniele Varrazzo]

Daniele Varrazzo  added the comment:

FYI, will try to use this API in psycopg3, which supports the PostgreSQL 
decimal binary format. Thank you very much: it seems exactly what needed.

Binary conversion with Python Decimal currently has disappointing performances 
and is slower than the text format conversion. This is likely caused by the use 
of Decimal.as_tuple(), which creates tuples for the return value and the digits 
and requires Python calls to access their values.

I have considered using libmpdec directly: personally I wouldn't be opposed to 
that, but the additional dependency on libmpdec-dev would earn the project no 
new fan :\

Ref. https://github.com/psycopg/psycopg3/issues/54

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[issue41324] Add a minimal decimal capsule API

[Antoine Pitrou]

Antoine Pitrou  added the comment:

For the record, this is going to be reverted at Stefan's request in issue43422.

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[issue41324] Add a minimal decimal capsule API

[Antoine Pitrou]

Antoine Pitrou  added the comment:

@mattip, see issue43422

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[issue41324] Add a minimal decimal capsule API

[mattip]

mattip  added the comment:

Was expanding the C-API discussed on the mailing list or in any wider forum? It 
seems vstinner is working hard to reduce the public API exposure while this 
issue + PR makes it even larger. Please reconsider putting this in for 3.10.

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nosy: +mattip

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Change by Stefan Krah :


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components: +C API -Extension Modules
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Stefan Krah  added the comment:


New changeset 39042e00ab01d6521548c1b7cc6554c09f4389ff by Stefan Krah in branch 
'master':
bpo-41324 Add a minimal decimal capsule API (#21519)
https://github.com/python/cpython/commit/39042e00ab01d6521548c1b7cc6554c09f4389ff


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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Stefan Krah  added the comment:

I'm happy with the API, except that --with-system-libmpdec is naturally
broken.  So I've to release a new libmpdec, which I'd rather do soon
because I don't want to revisit this later.

Antoine has looked at the API.  If anyone else has requests or objections,
now would be a good time to raise concerns.  These two functions are
the centerpiece of the PR:

   mpd_uint128_triple_t PyDec_AsUint128Triple(const PyObject *dec)
   PyObject *PyDec_FromUint128Triple(const mpd_uint128_triple_t *triple)

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[issue41324] Add a minimal decimal capsule API

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


--
title: En az ondalık kapsül API ekleme -> Add a minimal decimal capsule API

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Stefan Krah  added the comment:

It looks like the API would be usable, so the PR now has documentation.

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[issue41324] Add a minimal decimal capsule API

[Antoine Pitrou]

Antoine Pitrou  added the comment:

I probably won't try it out explicitly (it's basically cumbersome for us to 
test with non-release Pythons, because of our dependencies to Numpy and 
Cython), but reviewing the API should be enough anyway.

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Stefan Krah  added the comment:

Adding Daniele Varrazzo, in case this is useful for the PostgreSQL
adapter.

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nosy: +piro

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Stefan Krah  added the comment:

Also as a note for Mark and Raymond: This API is for exact conversions
and avoids the use of the context except for raising ConversionSyntax.

I'll add documentation once Antoine has tried it out for his use case.

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Change by Stefan Krah :


--
type:  -> enhancement

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

New submission from Stefan Krah :

This adds a minimal decimal capsule API.  As can be seen from the patch,
adding anything to decimal while doing it properly is quite labor and
testing intensive, so the intent is to *keep* the API minimal!

That said, some functions are really necessary:

  1) PyDec_TypeCheck() -- for obvious reasons.

  2) PyDec_Alloc() -- create new decimals.

  3) PyDec_Get()   -- get the mpd_t, enables the use of all 
libmpdec functions.

  4) PyDec_AsUint128Triple()   -- export the decimal as (sign, hi, lo, exp).

  5) PyDec_FromUint128Triple() -- create a decimal from (sign, hi, lo, exp).


4) and 5) have been requested by Antoine for a real world use case.  (hi, lo)
is the coefficient as a __uint128_t split in two uint64_t.


Antoine, could you verify that this is sufficient for the database use case?

--
nosy: +mark.dickinson, pitrou, rhettinger

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Change by Stefan Krah :


--
keywords: +patch
pull_requests: +20656
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/21519

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[issue41324] Add a minimal decimal capsule API

[Stefan Krah]

Change by Stefan Krah :


--
assignee: skrah
components: Extension Modules
nosy: skrah
priority: normal
severity: normal
stage: needs patch
status: open
title: Add a minimal decimal capsule API
versions: Python 3.10

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