BUG: Calling squeeze on a slice of a memmap raises cryptic error #25278
Description
Describe the issue:
Calling .squeeze() on a slice of a memmap that has shape (1,) raises
RuntimeError: ndarray subclass __array_wrap__ method returned an object which was not an instance of an ndarray subclass
Reproduce the code example:
import numpy as np
import struct
# set up file
filename = 'ex.bin'
with open(filename, 'wb') as f:
f.write(bytearray(struct.pack('d', 3.14)))
f.write(bytearray(struct.pack('d', 6.28)))
# mmap file
arr = np.memmap(filename, dtype=np.float64, mode='r', shape=(2,1))
print(arr)
print(arr.squeeze()) # works
print(arr[1:2,0])
print(np.array(arr)[1:2,0].squeeze()) # works
print(arr[1:2,0].squeeze()) # failsError message:
Traceback (most recent call last):
File "/home/brian/Dev/cpp/ffistan/repr.py", line 18, in <module>
print(arr[1:2,0].squeeze()) # fails
RuntimeError: ndarray subclass __array_wrap__ method returned an object which was not an instance of an ndarray subclassRuntime information:
>>> import sys, numpy; print(numpy.__version__); print(sys.version)
1.26.2
3.9.13 | packaged by conda-forge | (main, May 27 2022, 16:56:21)
[GCC 10.3.0]
>>> print(numpy.show_runtime())
WARNING: `threadpoolctl` not found in system! Install it by `pip install threadpoolctl`. Once installed, try `np.show_runtime` again for more detailed build information
[{'numpy_version': '1.26.2',
'python': '3.9.13 | packaged by conda-forge | (main, May 27 2022, '
'16:56:21) \n'
'[GCC 10.3.0]',
'uname': uname_result(system='Linux', node='FlatTop', release='6.2.0-37-generic', version='#38~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Nov 2 18:01:13 UTC 2', machine='x86_64')},
{'simd_extensions': {'baseline': ['SSE', 'SSE2', 'SSE3'],
'found': ['SSSE3',
'SSE41',
'POPCNT',
'SSE42',
'AVX',
'F16C',
'FMA3',
'AVX2',
'AVX512F',
'AVX512CD',
'AVX512_SKX',
'AVX512_CLX',
'AVX512_CNL',
'AVX512_ICL'],
'not_found': ['AVX512_KNL', 'AVX512_KNM']}}]
None
Context for the issue:
This operation seems well-defined for normal arrays but fails for memmaps. This violates the sentence The memmap object can be used anywhere an ndarray is accepted. in the documentation, and makes it difficult to write a library which relies on squeeze in a generic way which is ambivalent to whether the user provided an array or memmap