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  1. Apache Arrow
  2. ARROW-3228

[Python] Immutability of bytes is ignored

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      Description

      Creating a pyarrow.Buffer from Python bytes allows in-place changes of immutable Python strings:

      >>> 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

      Notice that numpy.frombuffer respects immutability of bytes:
      {{}}

      >>> 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

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              • Assignee:
                wesmckinn Wes McKinney
                Reporter:
                pearu Pearu Peterson
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