ENH: __array_function__ updates for NumPy 1.17.0

- Always enable __array_function__ overrides.
- Remove special cases for Python 2 compatibility.
- Document these changes in 1.17.0-notes.rst.

It will be good to see ASV numbers to understand the performance implications
of these changes. If need be, we can speed up NumPy functions internally by
using non-dispatched functions (with ``.__wrapped__``).

6 files changed, 5 insertions, 51 deletions

diff --git a/numpy/core/overrides.py b/numpy/core/overrides.py
index c55174ecd..46097f39c 100644
--- a/numpy/core/overrides.py
+++ b/numpy/core/overrides.py
@@ -8,10 +8,6 @@ from numpy.core._multiarray_umath import (
 from numpy.compat._inspect import getargspec
 
 
-ENABLE_ARRAY_FUNCTION = bool(
-    int(os.environ.get('NUMPY_EXPERIMENTAL_ARRAY_FUNCTION', 0)))
-
-
 add_docstring(
     implement_array_function,
     """
@@ -141,16 +137,6 @@ def array_function_dispatch(dispatcher, module=None, verify=True,
     Function suitable for decorating the implementation of a NumPy function.
     """
 
-    if not ENABLE_ARRAY_FUNCTION:
-        # __array_function__ requires an explicit opt-in for now
-        def decorator(implementation):
-            if module is not None:
-                implementation.__module__ = module
-            if docs_from_dispatcher:
-                add_docstring(implementation, dispatcher.__doc__)
-            return implementation
-        return decorator
-
     def decorator(implementation):
         if verify:
             verify_matching_signatures(implementation, dispatcher)
@@ -167,10 +153,6 @@ def array_function_dispatch(dispatcher, module=None, verify=True,
         if module is not None:
             public_api.__module__ = module
 
-        # TODO: remove this when we drop Python 2 support (functools.wraps
-        # adds __wrapped__ automatically in later versions)
-        public_api.__wrapped__ = implementation
-
         return public_api
 
     return decorator
diff --git a/numpy/core/shape_base.py b/numpy/core/shape_base.py
index f8332c362..08e07bb66 100644
--- a/numpy/core/shape_base.py
+++ b/numpy/core/shape_base.py
@@ -217,11 +217,6 @@ def _arrays_for_stack_dispatcher(arrays, stacklevel=4):
     return arrays
 
 
-def _warn_for_nonsequence(arrays):
-    if not overrides.ENABLE_ARRAY_FUNCTION:
-        _arrays_for_stack_dispatcher(arrays, stacklevel=4)
-
-
 def _vhstack_dispatcher(tup):
     return _arrays_for_stack_dispatcher(tup)
 
@@ -279,7 +274,6 @@ def vstack(tup):
            [4]])
 
     """
-    _warn_for_nonsequence(tup)
     return _nx.concatenate([atleast_2d(_m) for _m in tup], 0)
 
 
@@ -331,7 +325,6 @@ def hstack(tup):
            [3, 4]])
 
     """
-    _warn_for_nonsequence(tup)
     arrs = [atleast_1d(_m) for _m in tup]
     # As a special case, dimension 0 of 1-dimensional arrays is "horizontal"
     if arrs and arrs[0].ndim == 1:
@@ -406,7 +399,6 @@ def stack(arrays, axis=0, out=None):
            [3, 4]])
 
     """
-    _warn_for_nonsequence(arrays)
     arrays = [asanyarray(arr) for arr in arrays]
     if not arrays:
         raise ValueError('need at least one array to stack')
diff --git a/numpy/core/tests/test_overrides.py b/numpy/core/tests/test_overrides.py
index 8f1c16539..4d1844b8d 100644
--- a/numpy/core/tests/test_overrides.py
+++ b/numpy/core/tests/test_overrides.py
@@ -8,16 +8,11 @@ from numpy.testing import (
     assert_, assert_equal, assert_raises, assert_raises_regex)
 from numpy.core.overrides import (
     _get_implementing_args, array_function_dispatch,
-    verify_matching_signatures, ENABLE_ARRAY_FUNCTION)
+    verify_matching_signatures)
 from numpy.core.numeric import pickle
 import pytest
 
 
-requires_array_function = pytest.mark.skipif(
-    not ENABLE_ARRAY_FUNCTION,
-    reason="__array_function__ dispatch not enabled.")
-
-
 def _return_not_implemented(self, *args, **kwargs):
     return NotImplemented
 
@@ -35,7 +30,6 @@ def dispatched_two_arg(array1, array2):
     return 'original'
 
 
-@requires_array_function
 class TestGetImplementingArgs(object):
 
     def test_ndarray(self):
@@ -147,7 +141,6 @@ class TestGetImplementingArgs(object):
             _get_implementing_args(relevant_args)
 
 
-@requires_array_function
 class TestNDArrayArrayFunction(object):
 
     def test_method(self):
@@ -206,7 +199,6 @@ class TestNDArrayArrayFunction(object):
                                      args=(array,), kwargs={})
 
 
-@requires_array_function
 class TestArrayFunctionDispatch(object):
 
     def test_pickle(self):
@@ -246,7 +238,6 @@ class TestArrayFunctionDispatch(object):
             dispatched_one_arg(array)
 
 
-@requires_array_function
 class TestVerifyMatchingSignatures(object):
 
     def test_verify_matching_signatures(self):
@@ -299,7 +290,6 @@ def _new_duck_type_and_implements():
     return (MyArray, implements)
 
 
-@requires_array_function
 class TestArrayFunctionImplementation(object):
 
     def test_one_arg(self):
@@ -376,12 +366,10 @@ class TestNumPyFunctions(object):
         assert_equal(np.fft.fft.__module__, 'numpy.fft')
         assert_equal(np.linalg.solve.__module__, 'numpy.linalg')
 
-    @pytest.mark.skipif(sys.version_info[0] < 3, reason="Python 3 only")
     def test_inspect_sum(self):
         signature = inspect.signature(np.sum)
         assert_('axis' in signature.parameters)
 
-    @requires_array_function
     def test_override_sum(self):
         MyArray, implements = _new_duck_type_and_implements()
 
diff --git a/numpy/lib/shape_base.py b/numpy/lib/shape_base.py
index e088a6c4a..ac2a25604 100644
--- a/numpy/lib/shape_base.py
+++ b/numpy/lib/shape_base.py
@@ -11,8 +11,7 @@ from numpy.core.fromnumeric import product, reshape, transpose
 from numpy.core.multiarray import normalize_axis_index
 from numpy.core import overrides
 from numpy.core import vstack, atleast_3d
-from numpy.core.shape_base import (
-    _arrays_for_stack_dispatcher, _warn_for_nonsequence)
+from numpy.core.shape_base import _arrays_for_stack_dispatcher
 from numpy.lib.index_tricks import ndindex
 from numpy.matrixlib.defmatrix import matrix  # this raises all the right alarm bells
 
@@ -630,7 +629,6 @@ def column_stack(tup):
            [3, 4]])
 
     """
-    _warn_for_nonsequence(tup)
     arrays = []
     for v in tup:
         arr = array(v, copy=False, subok=True)
@@ -695,7 +693,6 @@ def dstack(tup):
            [[3, 4]]])
 
     """
-    _warn_for_nonsequence(tup)
     return _nx.concatenate([atleast_3d(_m) for _m in tup], 2)
 
 
diff --git a/numpy/lib/ufunclike.py b/numpy/lib/ufunclike.py
index 5c411e8c8..8452604d9 100644
--- a/numpy/lib/ufunclike.py
+++ b/numpy/lib/ufunclike.py
@@ -8,7 +8,7 @@ from __future__ import division, absolute_import, print_function
 __all__ = ['fix', 'isneginf', 'isposinf']
 
 import numpy.core.numeric as nx
-from numpy.core.overrides import array_function_dispatch, ENABLE_ARRAY_FUNCTION
+from numpy.core.overrides import array_function_dispatch
 import warnings
 import functools
 
@@ -55,10 +55,6 @@ def _fix_out_named_y(f):
     return func
 
 
-if not ENABLE_ARRAY_FUNCTION:
-    _fix_out_named_y = _deprecate_out_named_y
-
-
 @_deprecate_out_named_y
 def _dispatcher(x, out=None):
     return (x, out)
diff --git a/numpy/testing/tests/test_utils.py b/numpy/testing/tests/test_utils.py
index c376a3852..9081f3d6e 100644
--- a/numpy/testing/tests/test_utils.py
+++ b/numpy/testing/tests/test_utils.py
@@ -186,9 +186,8 @@ class TestArrayEqual(_GenericTest):
 
         a = np.array([1., 2.]).view(MyArray)
         b = np.array([2., 3.]).view(MyArray)
-        if np.core.overrides.ENABLE_ARRAY_FUNCTION:
-            with assert_raises(TypeError):
-                np.all(a)
+        with assert_raises(TypeError):
+            np.all(a)
         self._test_equal(a, a)
         self._test_not_equal(a, b)
         self._test_not_equal(b, a)