Fix undefined memoryview format (#2223)

* Fix undefined memoryview format

* Add missing <algorithm> header

* Add workaround for py27 array compatibility

* Workaround py27 memoryview behavior

* Fix memoryview constructor from buffer_info

* Workaround PyMemoryView_FromMemory availability in py27

* Fix up memoryview tests

* Update memoryview test from buffer to check signedness

* Use static factory method to create memoryview

* Remove ndim arg from memoryview::frombuffer and add tests

* Allow ndim=0 memoryview and documentation fixup

* Use void* to align to frombuffer method signature

* Add const variants of frombuffer and frommemory

* Add memory view section in doc

* Fix docs

* Add test for null buffer

* Workaround py27 nullptr behavior in test

* Rename frombuffer to from_buffer

tests/test_pytypes.py

@@ -278,3 +278,70 @@ def test_number_protocol():
 def test_list_slicing():
     li = list(range(100))
     assert li[::2] == m.test_list_slicing(li)
+
+
+@pytest.mark.parametrize('method, args, fmt, expected_view', [
+    (m.test_memoryview_object, (b'red',), 'B', b'red'),
+    (m.test_memoryview_buffer_info, (b'green',), 'B', b'green'),
+    (m.test_memoryview_from_buffer, (False,), 'h', [3, 1, 4, 1, 5]),
+    (m.test_memoryview_from_buffer, (True,), 'H', [2, 7, 1, 8]),
+    (m.test_memoryview_from_buffer_nativeformat, (), '@i', [4, 7, 5]),
+])
+def test_memoryview(method, args, fmt, expected_view):
+    view = method(*args)
+    assert isinstance(view, memoryview)
+    assert view.format == fmt
+    if isinstance(expected_view, bytes) or sys.version_info[0] >= 3:
+        view_as_list = list(view)
+    else:
+        # Using max to pick non-zero byte (big-endian vs little-endian).
+        view_as_list = [max([ord(c) for c in s]) for s in view]
+    assert view_as_list == list(expected_view)
+
+
+@pytest.mark.skipif(
+    not hasattr(sys, 'getrefcount'),
+    reason='getrefcount is not available')
+@pytest.mark.parametrize('method', [
+    m.test_memoryview_object,
+    m.test_memoryview_buffer_info,
+])
+def test_memoryview_refcount(method):
+    buf = b'\x0a\x0b\x0c\x0d'
+    ref_before = sys.getrefcount(buf)
+    view = method(buf)
+    ref_after = sys.getrefcount(buf)
+    assert ref_before < ref_after
+    assert list(view) == list(buf)
+
+
+def test_memoryview_from_buffer_empty_shape():
+    view = m.test_memoryview_from_buffer_empty_shape()
+    assert isinstance(view, memoryview)
+    assert view.format == 'B'
+    if sys.version_info.major < 3:
+        # Python 2 behavior is weird, but Python 3 (the future) is fine.
+        assert bytes(view).startswith(b'<memory at ')
+    else:
+        assert bytes(view) == b''
+
+
+def test_test_memoryview_from_buffer_invalid_strides():
+    with pytest.raises(RuntimeError):
+        m.test_memoryview_from_buffer_invalid_strides()
+
+
+def test_test_memoryview_from_buffer_nullptr():
+    if sys.version_info.major < 3:
+        m.test_memoryview_from_buffer_nullptr()
+    else:
+        with pytest.raises(ValueError):
+            m.test_memoryview_from_buffer_nullptr()
+
+
+@pytest.mark.skipif(sys.version_info.major < 3, reason='API not available')
+def test_memoryview_from_memory():
+    view = m.test_memoryview_from_memory()
+    assert isinstance(view, memoryview)
+    assert view.format == 'B'
+    assert bytes(view) == b'\xff\xe1\xab\x37'