BUG: busday_count returns wrong results with begindates > enddates #23197
Description
Describe the issue:
According to the documentation, busday_count
Counts the number of valid days between begindates and enddates, not including the day of enddates. If enddates specifies a date value that is earlier than the corresponding begindates date value, the count will be negative.
However, in the implementation, if begindates is greater than enddates, the dates are swapped and the result is negated. This has the effect of including the enddates and excluding begindates, which contradicts the above spec.
Reproduce the code example:
from datetime import date
import numpy as np
d1 = date(1999, 12, 30)
d2 = date(2000, 1, 1)
assert np.busday_count(d1, d2) == 2 # 1999-12-30 and 1999-12-31
assert np.busday_count(d2, d1) == -1 # 1999-12-31 only, end date is excludedError message:
Traceback (most recent call last):
File "/home/elt/code/numpy-test/busday.py", line 8, in <module>
assert np.busday_count(d2, d1) == -1
AssertionErrorRuntime information:
Output from import sys, numpy; print(numpy.__version__); print(sys.version)
1.24.1
3.10.6 (main, Nov 14 2022, 16:10:14) [GCC 11.3.0]Output from print(numpy.show_runtime())
[{'simd_extensions': {'baseline': ['SSE', 'SSE2', 'SSE3'],
'found': ['SSSE3',
'SSE41',
'POPCNT',
'SSE42',
'AVX',
'F16C',
'FMA3',
'AVX2'],
'not_found': ['AVX512F',
'AVX512CD',
'AVX512_KNL',
'AVX512_KNM',
'AVX512_SKX',
'AVX512_CLX',
'AVX512_CNL',
'AVX512_ICL']}},
{'architecture': 'Haswell',
'filepath': '/home/elt/.local/lib/python3.10/site-packages/numpy.libs/libopenblas64_p-r0-15028c96.3.21.so',
'internal_api': 'openblas',
'num_threads': 16,
'prefix': 'libopenblas',
'threading_layer': 'pthreads',
'user_api': 'blas',
'version': '0.3.21'}]Context for the issue:
This breaks the invariant that
count = numpy.busday_count(d1, d2)
numpy.busday_offset(d1, count, "forward" if count > 0 else "backward") == d2for every d1 and every valid d2.