BUG: Provide correct format in Py_buffer for scalars (#10564)

Unifies scalar and ndarray pep3118 format string generation

1 files changed, 84 insertions, 0 deletions

diff --git a/numpy/core/tests/test_scalarbuffer.py b/numpy/core/tests/test_scalarbuffer.py
new file mode 100644
index 000000000..cd887f2fb
--- /dev/null
+++ b/numpy/core/tests/test_scalarbuffer.py
@@ -0,0 +1,84 @@
+"""
+Test scalar buffer interface adheres to PEP 3118
+"""
+import sys
+import numpy as np
+from numpy.testing import run_module_suite, assert_, assert_equal, dec
+
+# PEP3118 format strings for native (standard alignment and byteorder) types
+scalars_and_codes = [
+    (np.bool_, '?'),
+    (np.byte, 'b'),
+    (np.short, 'h'),
+    (np.intc, 'i'),
+    (np.int_, 'l'),
+    (np.longlong, 'q'),
+    (np.ubyte, 'B'),
+    (np.ushort, 'H'),
+    (np.uintc, 'I'),
+    (np.uint, 'L'),
+    (np.ulonglong, 'Q'),
+    (np.half, 'e'),
+    (np.single, 'f'),
+    (np.double, 'd'),
+    (np.longdouble, 'g'),
+    (np.csingle, 'Zf'),
+    (np.cdouble, 'Zd'),
+    (np.clongdouble, 'Zg'),
+]
+
+
+class TestScalarPEP3118(object):
+    skip_if_no_buffer_interface = dec.skipif(sys.version_info.major < 3,
+                "scalars do not implement buffer interface in Python 2")
+
+    @skip_if_no_buffer_interface
+    def test_scalar_match_array(self):
+        for scalar, _ in scalars_and_codes:
+            x = scalar()
+            a = np.array([], dtype=np.dtype(scalar))
+            mv_x = memoryview(x)
+            mv_a = memoryview(a)
+            assert_equal(mv_x.format, mv_a.format)
+
+    @skip_if_no_buffer_interface
+    def test_scalar_dim(self):
+        for scalar, _ in scalars_and_codes:
+            x = scalar()
+            mv_x = memoryview(x)
+            assert_equal(mv_x.itemsize, np.dtype(scalar).itemsize)
+            assert_equal(mv_x.ndim, 0)
+            assert_equal(mv_x.shape, ())
+            assert_equal(mv_x.strides, ())
+            assert_equal(mv_x.suboffsets, ())
+
+    @skip_if_no_buffer_interface
+    def test_scalar_known_code(self):
+        for scalar, code in scalars_and_codes:
+            x = scalar()
+            mv_x = memoryview(x)
+            assert_equal(mv_x.format, code)
+
+    @skip_if_no_buffer_interface
+    def test_void_scalar_structured_data(self):
+        dt = np.dtype([('name', np.unicode_, 16), ('grades', np.float64, (2,))])
+        x = np.array(('ndarray_scalar', (1.2, 3.0)), dtype=dt)[()]
+        assert_(isinstance(x, np.void))
+        mv_x = memoryview(x)
+        expected_size = 16 * np.dtype((np.unicode_, 1)).itemsize
+        expected_size += 2 * np.dtype((np.float64, 1)).itemsize
+        assert_equal(mv_x.itemsize, expected_size)
+        assert_equal(mv_x.ndim, 0)
+        assert_equal(mv_x.shape, ())
+        assert_equal(mv_x.strides, ())
+        assert_equal(mv_x.suboffsets, ())
+
+        # check scalar format string against ndarray format string
+        a = np.array([('Sarah', (8.0, 7.0)), ('John', (6.0, 7.0))], dtype=dt)
+        assert_(isinstance(a, np.ndarray))
+        mv_a = memoryview(a)
+        assert_equal(mv_x.itemsize, mv_a.itemsize)
+        assert_equal(mv_x.format, mv_a.format)
+
+if __name__ == "__main__":
+    run_module_suite()