Add support for copy kwarg in astype to match Array API

CHANGELOG.md

@@ -26,6 +26,12 @@ Remember to align the itemized text with the first line of an item within a list
   * The `device()` method of JAX arrays has been removed, after being deprecated
     since JAX v0.4.21. Use `arr.devices()` instead.
 
+* Bug fixes
+  * {func}`jax.numpy.astype` will now always return a copy when `copy=True`.
+    Previously, no copy would be made when the output array would have the same
+    dtype as the input array. This may result in some increased memory usage.
+    To prevent copying when possible, set `copy=None`. To error when a copy is
+    required, set `copy=False`.
 
 ## jaxlib 0.4.27
 

jax/_src/numpy/array_methods.py

@@ -31,11 +31,13 @@
 import numpy as np
 import jax
 from jax import lax
+from jax.sharding import Sharding
 from jax._src import core
 from jax._src import dtypes
 from jax._src.api_util import _ensure_index_tuple
 from jax._src.array import ArrayImpl
 from jax._src.lax import lax as lax_internal
+from jax._src.lib import xla_client as xc
 from jax._src.numpy import lax_numpy
 from jax._src.numpy import reductions
 from jax._src.numpy import ufuncs
@@ -55,15 +57,15 @@
 # functions, which can themselves handle instances from any of these classes.
 
 
-def _astype(arr: ArrayLike, dtype: DTypeLike) -> Array:
+def _astype(arr: ArrayLike, dtype: DTypeLike, copy: bool = True, device: xc.Device | Sharding | None = None) -> Array:
   """Copy the array and cast to a specified dtype.
 
   This is implemented via :func:`jax.lax.convert_element_type`, which may
   have slightly different behavior than :meth:`numpy.ndarray.astype` in
   some cases. In particular, the details of float-to-int and int-to-float
   casts are implementation dependent.
   """
-  return lax_numpy.astype(arr, dtype)
+  return lax_numpy.astype(arr, dtype, copy=copy, device=device)
 
 
 def _nbytes(arr: ArrayLike) -> int:

jax/_src/numpy/lax_numpy.py

@@ -2262,17 +2262,43 @@ def _convert_to_array_if_dtype_fails(x: ArrayLike) -> ArrayLike:
 In particular, the details of float-to-int and int-to-float casts are
 implementation dependent.
 """)
-def astype(x: ArrayLike, dtype: DTypeLike | None, /, *, copy: bool = True) -> Array:
+def astype(x: ArrayLike, dtype: DTypeLike | None,
+           /, *, copy: bool = True,
+           device: xc.Device | Sharding | None = None) -> Array:
   util.check_arraylike("astype", x)
   x_arr = asarray(x)
-  del copy  # unused in JAX
   if dtype is None:
     dtype = dtypes.canonicalize_dtype(float_)
   dtypes.check_user_dtype_supported(dtype, "astype")
+  if (
+    issubdtype(x_arr.dtype, complexfloating)
+    and dtypes.isdtype(dtype, ("integral", "real floating"))
+  ):
+    warnings.warn(
+      "Casting from complex to real dtypes will soon raise a ValueError. "
+      "Please first use jnp.real or jnp.imag to take the real/imaginary "
+      "component of your input.",
+      DeprecationWarning, stacklevel=2
+    )
+
+  out = x_arr
   # convert_element_type(complex, bool) has the wrong semantics.
   if np.dtype(dtype) == bool and issubdtype(x_arr.dtype, complexfloating):
-    return (x_arr != _lax_const(x_arr, 0))
-  return lax.convert_element_type(x_arr, dtype)
+    out = (x_arr != _lax_const(x_arr, 0))
+  out = _place_array(out, device=device, copy=copy)
+
+  # We offer a more specific warning than the usual ComplexWarning so we prefer
+  # to issue our warning.
+  with warnings.catch_warnings():
+    warnings.simplefilter("ignore", ComplexWarning)
+    return lax.convert_element_type(out, dtype)
+
+def _place_array(x, device=None, copy=None):
+  # TODO(micky774): Implement in future PRs as we formalize device placement
+  # semantics
+  if copy:
+    return _array_copy(x)
+  return x
 
 
 @util.implements(np.asarray, lax_description=_ARRAY_DOC)

jax/experimental/array_api/_data_type_functions.py

@@ -12,13 +12,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import annotations
+
 import builtins
 import functools
 from typing import NamedTuple
 import jax
 import jax.numpy as jnp
 
 
+from jax._src.lib import xla_client as xc
+from jax._src.sharding import Sharding
+from jax._src import dtypes as _dtypes
 from jax.experimental.array_api._dtypes import (
   bool, int8, int16, int32, int64, uint8, uint16, uint32, uint64,
   float32, float64, complex64, complex128
@@ -124,8 +129,19 @@ def _promote_types(t1, t2):
     raise ValueError("No promotion path for {t1} & {t2}")
 
 
-def astype(x, dtype, /, *, copy=True):
-  return jnp.array(x, dtype=dtype, copy=copy)
+def astype(x, dtype, /, *, copy: builtins.bool = True, device: xc.Device | Sharding | None = None):
+  src_dtype = x.dtype if hasattr(x, "dtype") else _dtypes.dtype(x)
+  if (
+    src_dtype is not None
+    and _dtypes.isdtype(src_dtype, "complex floating")
+    and _dtypes.isdtype(dtype, ("integral", "real floating"))
+  ):
+    raise ValueError(
+      "Casting from complex to non-complex dtypes is not permitted. Please "
+      "first use jnp.real or jnp.imag to take the real/imaginary component of "
+      "your input."
+    )
+  return jnp.astype(x, dtype, copy=copy, device=device)
 
 
 def can_cast(from_, to, /):

jax/numpy/__init__.pyi

@@ -13,6 +13,8 @@ from jax._src.typing import (
     Array, ArrayLike, DType, DTypeLike,
     DimSize, DuckTypedArray, Shape, DeprecatedArg
 )
+from jax._src.sharding import Sharding
+from jax._src.lib import xla_client as xc
 from jax.numpy import fft as fft, linalg as linalg
 from jax.sharding import Sharding as _Sharding
 import numpy as _np
@@ -115,7 +117,7 @@ def asarray(
 ) -> Array: ...
 def asin(x: ArrayLike, /) -> Array: ...
 def asinh(x: ArrayLike, /) -> Array: ...
-def astype(a: ArrayLike, dtype: Optional[DTypeLike], /, *, copy: builtins.bool = ...) -> Array: ...
+def astype(a: ArrayLike, dtype: Optional[DTypeLike], /, *, copy: builtins.bool = ..., device: xc.Device | Sharding | None = ...) -> Array: ...
 def atan(x: ArrayLike, /) -> Array: ...
 def atan2(x: ArrayLike, y: ArrayLike, /) -> Array: ...
 def atanh(x: ArrayLike, /) -> Array: ...

tests/lax_numpy_test.py

@@ -3840,6 +3840,26 @@ def testAstypeBool(self, from_dtype, use_method, to_dtype='bool'):
     self._CheckAgainstNumpy(np_op, jnp_op, args_maker)
     self._CompileAndCheck(jnp_op, args_maker)
 
+  @jtu.sample_product(
+    change_dtype=[True, False],
+    copy=[True, False],
+  )
+  def testAstypeCopy(self, change_dtype, copy):
+    dtype = 'float32' if change_dtype else 'int32'
+    expect_copy = change_dtype or copy
+    x = jnp.arange(5, dtype='int32')
+    y = x.astype(dtype, copy=copy)
+
+    assert y.dtype == dtype
+    y.delete()
+    assert x.is_deleted() != expect_copy
+
+  def testAstypeComplexDowncast(self):
+    x = jnp.array(2.0+1.5j, dtype='complex64')
+    msg = "Casting from complex to non-complex dtypes will soon raise "
+    with self.assertWarns(DeprecationWarning, msg=msg):
+      x.astype('float32')
+
   def testAstypeInt4(self):
     # Test converting from int4 to int8
     x = np.array([1, -2, -3, 4, -8, 7], dtype=jnp.int4)