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BUG: np.str_ treats '\x00' as the empty string. #28964

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lzlarryli opened this issue May 14, 2025 · 1 comment
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BUG: np.str_ treats '\x00' as the empty string. #28964

lzlarryli opened this issue May 14, 2025 · 1 comment
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00 - Bug 57 - Close? Issues which may be closable unless discussion continued

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@lzlarryli
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lzlarryli commented May 14, 2025 •
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Describe the issue:

'\x00' is a nonempty string but np.str_('\x00') is an empty string. This leads to strange behavior for parsing string arrays. For example,

In [1]: import numpy as np

In [2]: np.array(['\x00'])[0].encode('UTF-8'), ['\x00'][0].encode('UTF-8')
Out[2]: (b'', b'\x00')

In [3]: np.array(['\x01'])[0].encode('UTF-8'), ['\x01'][0].encode('UTF-8')
Out[3]: (b'\x01', b'\x01')

In [4]: np.array([''])[0].encode('UTF-8'), [''][0].encode('UTF-8')
Out[4]: (b'', b'')

Reproduce the code example:

import numpy as np
np.str_('\x00')

Error message:

np.str_('')  # This is wrong.

Python and NumPy Versions:

2.0.2
3.11.12 (main, Apr 9 2025, 08:55:54) [GCC 11.4.0]

Runtime Environment:

No response

Context for the issue:

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@ngoldbaum
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NumPy fixed-width string DTypes are null-padded, so there is no way to tell the difference between '\x00' and an empty string. This is a fundamental shortcoming of padding with trailing nulls like this.

If you use StringDType you can avoid this problem:

>>> np.array(['\x00'], dtype='T')[0].encode('UTF-8'), ['\x00'][0].encode('UTF-8')
(b'\x00', b'\x00')

Unfortunately we probably can't change the default string DType to be StringDType until NumPy 3.0.

@ngoldbaum ngoldbaum added the 57 - Close? Issues which may be closable unless discussion continued label May 14, 2025
@seberg seberg closed this as not planned Won't fix, can't repro, duplicate, stale May 14, 2025
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