TST: note on overwrite_input parameter in percentile

* added note that `overwrite_input` has not effect when `a` is not
  an array in the percentile function.
* added unit test to verify that no error is raised when `a` is not
  an array and `overwrite_input` is True.

2 files changed, 13 insertions, 2 deletions

diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index 9475c2edf..472d7eecc 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -2803,8 +2803,9 @@ def percentile(a, q, interpolation='linear', axis=None, out=None,
         the contents of the input array. In this case you should not make
         any assumptions about the content of the passed in array `a` after
         this function completes -- treat it as undefined. Default is False.
-        Note that, if `overwrite_input` is True and the input is not
-        already an array, an error will be raised.
+        Note that, if the `a` input is not already an array this parameter
+        will have no effect, `a` will be converted to an array internally
+        regardless of the value of this parameter.
 
     Returns
     -------
diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
index a69c82e18..dd0b6e0ee 100644
--- a/numpy/lib/tests/test_function_base.py
+++ b/numpy/lib/tests/test_function_base.py
@@ -1530,9 +1530,19 @@ class TestScoreatpercentile(TestCase):
         np.percentile(a, [50], overwrite_input=False)
         assert_equal(a, np.array([2, 3, 4, 1]))
 
+        a = np.array([2, 3, 4, 1])
         np.percentile(a, [50])
         assert_equal(a, np.array([2, 3, 4, 1]))
 
+    def test_percentile_overwrite(self):
+        a = np.array([2, 3, 4, 1])
+        b = np.percentile(a, [50], overwrite_input=True)
+        assert_equal(b, np.array([2.5]))
+
+        b = np.percentile([2, 3, 4, 1], [50], overwrite_input=True)
+        assert_equal(b, np.array([2.5]))
+
+
 
 class TestMedian(TestCase):
     def test_basic(self):