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https://issues.apache.org/jira/browse/ARROW-2153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16374730#comment-16374730
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ASF GitHub Bot commented on ARROW-2153:
---------------------------------------

cpcloud commented on issue #1618: ARROW-2153/ARROW-2160: [C++/Python]  Fix 
decimal precision inference
URL: https://github.com/apache/arrow/pull/1618#issuecomment-368086534
 
 
   Closed in favor of #1651 

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> [C++/Python] Decimal conversion not working for exponential notation
> --------------------------------------------------------------------
>
>                 Key: ARROW-2153
>                 URL: https://issues.apache.org/jira/browse/ARROW-2153
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>    Affects Versions: 0.8.0
>            Reporter: Antony Mayi
>            Assignee: Phillip Cloud
>            Priority: Major
>              Labels: pull-request-available
>
> {code:java}
> import pyarrow as pa
> import pandas as pd
> import decimal
> pa.Table.from_pandas(pd.DataFrame({'a': [decimal.Decimal('1.1'), 
> decimal.Decimal('2E+1')]}))
> {code}
>  
> {code:java}
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "pyarrow/table.pxi", line 875, in pyarrow.lib.Table.from_pandas 
> (/arrow/python/build/temp.linux-x86_64-3.6/lib.cxx:44927)
>   File 
> "/home/skadlec/.local/lib/python3.6/site-packages/pyarrow/pandas_compat.py", 
> line 350, in dataframe_to_arrays
>     convert_types)]
>   File 
> "/home/skadlec/.local/lib/python3.6/site-packages/pyarrow/pandas_compat.py", 
> line 349, in <listcomp>
>     for c, t in zip(columns_to_convert,
>   File 
> "/home/skadlec/.local/lib/python3.6/site-packages/pyarrow/pandas_compat.py", 
> line 345, in convert_column
>     return pa.array(col, from_pandas=True, type=ty)
>   File "pyarrow/array.pxi", line 170, in pyarrow.lib.array 
> (/arrow/python/build/temp.linux-x86_64-3.6/lib.cxx:29224)
>   File "pyarrow/array.pxi", line 70, in pyarrow.lib._ndarray_to_array 
> (/arrow/python/build/temp.linux-x86_64-3.6/lib.cxx:28465)
>   File "pyarrow/error.pxi", line 77, in pyarrow.lib.check_status 
> (/arrow/python/build/temp.linux-x86_64-3.6/lib.cxx:8270)
> pyarrow.lib.ArrowInvalid: Expected base ten digit or decimal point but found 
> 'E' instead.
> {code}
> In manual cases clearly we can write {{decimal.Decimal('20')}} instead of 
> {{decimal.Decimal('2E+1')}} but during arithmetical operations inside an 
> application the exponential notation can be produced out of control (it is 
> actually the _normalized_ form of the decimal number) plus for some values 
> the exponential notation is the only form expressing the significance so this 
> should be accepted.
> The [documentation|https://docs.python.org/3/library/decimal.html] suggests 
> using following transformation but that's only possible when the significance 
> information doesn't need to be kept:
> {code:java}
> def remove_exponent(d):
>     return d.quantize(Decimal(1)) if d == d.to_integral() else d.normalize()
> {code}



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