Add dpnp.ndarray.__format__ method (#2662)

The PR implements a special python method `__format__` for
`dpnp.ndarray`.

Author: antonwolfy

CHANGELOG.md

@@ -23,6 +23,7 @@ Also, that release drops support for Python 3.9, making Python 3.10 the minimum
 * Added implementation of `dpnp.ndarray.tofile` method [#2635](https://github.com/IntelPython/dpnp/pull/2635)
 * Extended `pre-commit` configuration with `pyupgrade`, `actionlint`, and `gersemi` hooks [#2658](https://github.com/IntelPython/dpnp/pull/2658)
 * Added implementation of `dpnp.ndarray.tobytes` method [#2656](https://github.com/IntelPython/dpnp/pull/2656)
+* Added implementation of `dpnp.ndarray.__format__` method [#2662](https://github.com/IntelPython/dpnp/pull/2662)
 
 ### Changed
 

doc/reference/ndarray.rst

@@ -449,3 +449,4 @@ String representations:
 
    ndarray.__str__
    ndarray.__repr__
+   ndarray.__format__

dpnp/dpnp_array.py

@@ -302,7 +302,9 @@ def __floordiv__(self, other, /):
         r"""Return :math:`\text{self // value}`."""
         return dpnp.floor_divide(self, other)
 
-    # '__format__',
+    def __format__(self, format_spec):
+        r"""Return :math:`\text{format(self, format_spec)}`."""
+        return format(self.asnumpy(), format_spec)
 
     def __ge__(self, other, /):
         r"""Return :math:`\text{self >= value}`."""

dpnp/tests/test_ndarray.py

@@ -108,6 +108,21 @@ def test_strides(self):
         assert xp.full_like(a, fill_value=6) not in a
 
 
+class TestFormat:
+    def test_basic(self):
+        a = numpy.array(3.14159)
+        ia = dpnp.array(a)
+
+        spec = ".3f"
+        assert_equal(format(ia, spec), format(a, spec))
+
+    @pytest.mark.parametrize("xp", [dpnp, numpy])
+    def test_1d(self, xp):
+        a = xp.array([3.14159])
+        with pytest.raises(TypeError, match="unsupported format string"):
+            _ = format(a, ".2f")
+
+
 class TestToBytes:
     @pytest.mark.parametrize("order", ["C", "F", "K", "A", None])
     def test_roundtrip_binary_str(self, order):

dpnp/tests/third_party/cupy/core_tests/test_ndarray.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import copy
 import unittest
 
@@ -649,21 +651,23 @@ def test_size_zero_dim_array_with_axis(self):
                 xp.size(x, 0)
 
 
-@pytest.mark.skip("python interface is not supported")
 class TestPythonInterface(unittest.TestCase):
 
+    @pytest.mark.skip("__bytes__ is not supported")
     @testing.for_all_dtypes()
     @testing.numpy_cupy_equal()
     def test_bytes_tobytes(self, xp, dtype):
         x = testing.shaped_arange((3, 4, 5), xp, dtype)
         return bytes(x)
 
+    @pytest.mark.skip("__bytes__ is not supported")
     @testing.for_all_dtypes()
     @testing.numpy_cupy_equal()
     def test_bytes_tobytes_empty(self, xp, dtype):
         x = xp.empty((0,), dtype)
         return bytes(x)
 
+    @pytest.mark.skip("__bytes__ is not supported")
     @testing.for_all_dtypes()
     @testing.numpy_cupy_equal()
     def test_bytes_tobytes_empty2(self, xp, dtype):
@@ -674,6 +678,7 @@ def test_bytes_tobytes_empty2(self, xp, dtype):
     # if scalar is of an integer dtype including bool_. It's spec is
     # bytes(int): bytes object of size given by the parameter initialized with
     # null bytes.
+    @pytest.mark.skip("__bytes__ is not supported")
     @testing.for_float_dtypes()
     @testing.numpy_cupy_equal()
     def test_bytes_tobytes_scalar_array(self, xp, dtype):