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https://issues.apache.org/jira/browse/ARROW-3228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16612892#comment-16612892
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Wes McKinney edited comment on ARROW-3228 at 9/13/18 12:25 AM:
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Apparently somewhere a mutability flag isn't being respected. Wasn't obvious at
a glance where the problem lies, see:
* https://github.com/apache/arrow/blob/master/cpp/src/arrow/python/common.cc#L61
* https://github.com/apache/arrow/blob/master/python/pyarrow/io.pxi#L831
was (Author: wesmckinn):
Apparently somewhere a mutability flag isn't being respected. What's obvious at
a glance where the problem lies, see:
* https://github.com/apache/arrow/blob/master/cpp/src/arrow/python/common.cc#L61
* https://github.com/apache/arrow/blob/master/python/pyarrow/io.pxi#L831
> [Python] Immutability of bytes is ignored
> -----------------------------------------
>
> Key: ARROW-3228
> URL: https://issues.apache.org/jira/browse/ARROW-3228
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Reporter: Pearu Peterson
> Priority: Major
> Fix For: 0.11.0
>
>
> Creating a pyarrow.Buffer from Python bytes allows in-place changes of
> immutable Python strings:
> {code:java}
> >>> import pyarrow as pa
> >>> import numpy as np
> >>> a = b'123456'
> >>> a[0] = 77 # bytes are immutable, so TypeError is expected
> TypeError: 'bytes' object does not support item assignment
> >>> b = pa.py_buffer(a) # but with pyarrow bytes can be changed in-place
> >>> arr = np.frombuffer(b, dtype=np.uint8)
> >>> arr[0] = 66 # change 'a' in-place, would expect error
> >>> a
> b'B23456'
> >>> hash(a)
> -4581532003987476523
> >>> arr[0] = 77
> >>> a
> b'M23456'
> >>> hash(a) # hash value stays constant while changing 'a'
> -4581532003987476523{code}
> {{Notice that numpy.frombuffer respects immutability of bytes:}}
> {{}}
> {code:java}
> >>> arr2 = np.frombuffer(a, dtype=np.uint8)
> >>> arr2
> array([77, 50, 51, 52, 53, 54], dtype=uint8)
> >>> arr2[0] = 88 # expecting error
> ValueError: assignment destination is read-only{code}
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