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import itertools
import numpy as np
def test_dtype_identity():
"""Confirm the intended behavior for ``asarray`` results.
The result of ``asarray()`` should have the dtype provided through the
keyword argument, when used. This forces unique array handles to be
produced for unique np.dtype objects, but (for equivalent dtypes), the
underlying data (the base object) is shared with the original array object.
Ref https://github.com/numpy/numpy/issues/1468
"""
int_array = np.array([1, 2, 3], dtype='i')
assert np.asarray(int_array) is int_array
# The character code resolves to the singleton dtype object provided
# by the numpy package.
assert np.asarray(int_array, dtype='i') is int_array
# Derive a dtype from n.dtype('i'), but add a metadata object to force
# the dtype to be distinct.
unequal_type = np.dtype('i', metadata={'spam': True})
annotated_int_array = np.asarray(int_array, dtype=unequal_type)
assert annotated_int_array is not int_array
assert annotated_int_array.base is int_array
# Create an equivalent descriptor with a new and distinct dtype instance.
equivalent_requirement = np.dtype('i', metadata={'spam': True})
annotated_int_array_alt = np.asarray(annotated_int_array,
dtype=equivalent_requirement)
assert unequal_type == equivalent_requirement
assert unequal_type is not equivalent_requirement
assert annotated_int_array_alt is not annotated_int_array
assert annotated_int_array_alt.dtype is equivalent_requirement
# Check the same logic for a pair of C types whose equivalence may vary
# between computing environments.
# Find an equivalent pair.
integer_type_codes = ('i', 'l', 'q')
integer_dtypes = [np.dtype(code) for code in integer_type_codes]
typeA = None
typeB = None
for typeA, typeB in itertools.permutations(integer_dtypes, r=2):
if typeA == typeB:
assert typeA is not typeB
break
assert isinstance(typeA, np.dtype) and isinstance(typeB, np.dtype)
# These ``asarray()`` calls may produce a new view or a copy,
# but never the same object.
long_int_array = np.asarray(int_array, dtype='l')
long_long_int_array = np.asarray(int_array, dtype='q')
assert long_int_array is not int_array
assert long_long_int_array is not int_array
assert np.asarray(long_int_array, dtype='q') is not long_int_array
array_a = np.asarray(int_array, dtype=typeA)
assert typeA == typeB
assert typeA is not typeB
assert array_a.dtype is typeA
assert array_a is not np.asarray(array_a, dtype=typeB)
assert np.asarray(array_a, dtype=typeB).dtype is typeB
assert array_a is np.asarray(array_a, dtype=typeB).base
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