DEP: Deprecate np.alen (#14181)

* Deprecate and fix tests for alen

3 files changed, 21 insertions, 9 deletions

diff --git a/numpy/core/fromnumeric.py b/numpy/core/fromnumeric.py
index 75a6bae7f..c9ea44425 100644
--- a/numpy/core/fromnumeric.py
+++ b/numpy/core/fromnumeric.py
@@ -2782,6 +2782,10 @@ def alen(a):
     7
 
     """
+    # NumPy 1.18.0, 2019-08-02
+    warnings.warn(
+        "`np.alen` is deprecated, use `len` instead",
+        DeprecationWarning, stacklevel=2)
     try:
         return len(a)
     except TypeError:
diff --git a/numpy/core/tests/test_deprecations.py b/numpy/core/tests/test_deprecations.py
index d6c870a94..e8aa0c70b 100644
--- a/numpy/core/tests/test_deprecations.py
+++ b/numpy/core/tests/test_deprecations.py
@@ -489,6 +489,12 @@ class TestBincount(_DeprecationTestCase):
         self.assert_deprecated(lambda: np.bincount([1, 2, 3], minlength=None))
 
 
+class TestAlen(_DeprecationTestCase):
+    # 2019-08-02, 1.18.0
+    def test_alen(self):
+        self.assert_deprecated(lambda: np.alen(np.array([1, 2, 3])))
+
+
 class TestGeneratorSum(_DeprecationTestCase):
     # 2018-02-25, 1.15.0
     def test_generator_sum(self):
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index bfc25e9ee..6a115f41b 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -6405,20 +6405,22 @@ class TestInner(object):
 
 class TestAlen(object):
     def test_basic(self):
-        m = np.array([1, 2, 3])
-        assert_equal(np.alen(m), 3)
+        with pytest.warns(DeprecationWarning):
+            m = np.array([1, 2, 3])
+            assert_equal(np.alen(m), 3)
 
-        m = np.array([[1, 2, 3], [4, 5, 7]])
-        assert_equal(np.alen(m), 2)
+            m = np.array([[1, 2, 3], [4, 5, 7]])
+            assert_equal(np.alen(m), 2)
 
-        m = [1, 2, 3]
-        assert_equal(np.alen(m), 3)
+            m = [1, 2, 3]
+            assert_equal(np.alen(m), 3)
 
-        m = [[1, 2, 3], [4, 5, 7]]
-        assert_equal(np.alen(m), 2)
+            m = [[1, 2, 3], [4, 5, 7]]
+            assert_equal(np.alen(m), 2)
 
     def test_singleton(self):
-        assert_equal(np.alen(5), 1)
+        with pytest.warns(DeprecationWarning):
+            assert_equal(np.alen(5), 1)
 
 
 class TestChoose(object):