| Lists: | pgsql-hackers |
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| From: | Marko Kreen <markokr(at)gmail(dot)com> |
|---|---|
| To: | Postgres Hackers List <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | [patch] PL/Python is too lossy with floats |
| Date: | 2015-03-03 14:32:16 |
| Message-ID: | [email protected] |
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PL/Python uses str(v) to convert float data, but is lossy
by design. Only repr(v) is guaranteed to have enough
precision to make floats roundtrip properly:
https://docs.python.org/2/library/functions.html#func-repr
https://docs.python.org/2/library/functions.html#str
Example:
$ python
>>> repr(100100100.654321)
'100100100.654321'
>>> str(100100100.654321)
'100100100.654'
Attached patch uses PyObject_Repr() for float data.
As it's annoying-to-debug problem and the patch is simple,
perhaps it's worth backporting?
--
marko
| Attachment | Content-Type | Size |
|---|---|---|
| plpy-float-repr.diff | text/x-diff | 1.9 KB |
| From: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
|---|---|
| To: | Marko Kreen <markokr(at)gmail(dot)com>, Postgres Hackers List <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [patch] PL/Python is too lossy with floats |
| Date: | 2015-03-11 19:49:50 |
| Message-ID: | [email protected] |
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On 3/3/15 9:32 AM, Marko Kreen wrote:
> PL/Python uses str(v) to convert float data, but is lossy
> by design. Only repr(v) is guaranteed to have enough
> precision to make floats roundtrip properly:
committed
| From: | Marko Kreen <markokr(at)gmail(dot)com> |
|---|---|
| To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Cc: | Postgres Hackers List <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [patch] PL/Python is too lossy with floats |
| Date: | 2015-06-01 09:34:41 |
| Message-ID: | CACMqXCKiaYm9iiFgc0SJ2rdgCpHMkaG94mrTfYKWQakdBeMoCQ@mail.gmail.com |
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On Wed, Mar 11, 2015 at 9:49 PM, Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
> On 3/3/15 9:32 AM, Marko Kreen wrote:
>> PL/Python uses str(v) to convert float data, but is lossy
>> by design. Only repr(v) is guaranteed to have enough
>> precision to make floats roundtrip properly:
>
> committed
In 9.3 and before, numeric is converted to float in PL/Python.
Please reconsider backporting.
--
marko
| From: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
|---|---|
| To: | Marko Kreen <markokr(at)gmail(dot)com> |
| Cc: | Postgres Hackers List <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [patch] PL/Python is too lossy with floats |
| Date: | 2015-06-10 02:04:25 |
| Message-ID: | [email protected] |
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On 6/1/15 5:34 AM, Marko Kreen wrote:
> On Wed, Mar 11, 2015 at 9:49 PM, Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
>> On 3/3/15 9:32 AM, Marko Kreen wrote:
>>> PL/Python uses str(v) to convert float data, but is lossy
>>> by design. Only repr(v) is guaranteed to have enough
>>> precision to make floats roundtrip properly:
>>
>> committed
>
> In 9.3 and before, numeric is converted to float in PL/Python.
>
> Please reconsider backporting.
It's been like this forever, so I don't think it's appropriate to
backpatch this.
| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Cc: | Marko Kreen <markokr(at)gmail(dot)com>, Postgres Hackers List <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [patch] PL/Python is too lossy with floats |
| Date: | 2015-06-10 02:28:35 |
| Message-ID: | [email protected] |
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Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> On 6/1/15 5:34 AM, Marko Kreen wrote:
>> Please reconsider backporting.
> It's been like this forever, so I don't think it's appropriate to
> backpatch this.
http://www.postgresql.org/docs/devel/static/plpython-data.html
states in so many words that floats are converted with str().
Presumably this needs an update in HEAD, but I would say that
the current behavior is per specification in all back branches.
regards, tom lane