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https://issues.apache.org/jira/browse/ARROW-2162?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16369492#comment-16369492
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ASF GitHub Bot commented on ARROW-2162:
---------------------------------------
pitrou commented on a change in pull request #1619: ARROW-2162: [Python/C++]
Decimal Values with too-high precision are multiplied by 100
URL: https://github.com/apache/arrow/pull/1619#discussion_r169167969
##########
File path: cpp/src/arrow/python/python-test.cc
##########
@@ -167,5 +167,14 @@ TEST(BuiltinConversionTest, TestMixedTypeFails) {
ASSERT_RAISES(UnknownError, ConvertPySequence(list, pool, &arr));
}
+TEST_F(DecimalTest, FromPythonDecimalRescale) {
+ Decimal128 value;
+ OwnedRef python_decimal(this->CreatePythonDecimal("1.0134"));
+ auto type = ::arrow::decimal(10, 2);
+ const auto& decimal_type = static_cast<const DecimalType&>(*type);
+ ASSERT_RAISES(Invalid,
internal::DecimalFromPythonDecimal(python_decimal.obj(),
Review comment:
I guess this would truncate? Perhaps add a comment? :)
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> [Python/C++] Decimal Values with too-high precision are multiplied by 100
> -------------------------------------------------------------------------
>
> Key: ARROW-2162
> URL: https://issues.apache.org/jira/browse/ARROW-2162
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++, Python
> Affects Versions: 0.8.0
> Reporter: Phillip Cloud
> Assignee: Phillip Cloud
> Priority: Major
> Labels: pull-request-available
> Fix For: 0.9.0
>
>
> From GitHub:
> This works as expected:
> {code}
> >>> pyarrow.array([decimal.Decimal('1.23')], pyarrow.decimal128(10,2))[0]
> Decimal('1.23')
> {code}
> Storing an extra digit of precision multiplies the stored value by a factor
> of 100:
> {code}
> >>> pyarrow.array([decimal.Decimal('1.234')], pyarrow.decimal128(10,2))[0]
> Decimal('123.40')
> {code}
> Ideally I would get an exception since the value I'm trying to store doesn't
> fit in the declared type of the array. It would be less good, but still ok,
> if the stored value were 1.23 (truncating the extra digit). I didn't expect
> pyarrow to silently store a value that differs from the original value by a
> factor of 100.
> I originally thought that the code was incorrectly multiplying through by an
> extra factor of 10**scale, but that doesn't seem to be the case. If I change
> the scale, it always seems to be a factor of 100
> {code}
> >>> pyarrow.array([decimal.Decimal('1.2345')], pyarrow.decimal128(10,3))[0]
> Decimal('123.450')
> I see the same behavior if I use floating point to initialize the array
> rather than Python's decimal type.
> {code}
> I searched for open github and JIRA for open issues but didn't find anything
> related to this. I am using pyarrow 0.8.0 on OS X 10.12.6 using python 2.7.14
> installed via Homebrew
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