Merge pull request #10826 from tylerjereddy/issue_10779_squeeze

BUG: np.squeeze() now respects older API axis expectation

3 files changed, 74 insertions, 6 deletions

diff --git a/doc/release/1.15.0-notes.rst b/doc/release/1.15.0-notes.rst
index 2a8c57351..cff75c477 100644
--- a/doc/release/1.15.0-notes.rst
+++ b/doc/release/1.15.0-notes.rst
@@ -55,6 +55,16 @@ All downstream users seem to use detect the `None` result from
 ``flatnotmasked_contiguous`` and replace it with ``[]``.
 These callers will continue to work as before.
 
+``np.squeeze`` now respects the API expectation of objects that do not handle an ``axis`` argument
+--------------------------------------------------------------------------------------------------
+Prior to version ``1.7.0`` ``np.squeeze`` did not have an ``axis`` argument and all empty axes were removed
+by default. After incorporation of an ``axis`` argument, it was possible to selectively squeeze single
+or multiple empty axes, but the old API expectation was not respected because the axes could still be
+selectively removed (silent success) in an object depending on the old API. The silent success is no
+longer possible, and objects expecting the old API are respected. The silent success was prevented
+by removing the interception of an otherwise-normal Exception when ``axis`` was provided to an object
+using the old API.
+
 
 C API changes
 =============
diff --git a/numpy/core/fromnumeric.py b/numpy/core/fromnumeric.py
index 63279ffb3..5f1aadbf5 100644
--- a/numpy/core/fromnumeric.py
+++ b/numpy/core/fromnumeric.py
@@ -1280,13 +1280,10 @@ def squeeze(a, axis=None):
         squeeze = a.squeeze
     except AttributeError:
         return _wrapit(a, 'squeeze')
-    try:
-        # First try to use the new axis= parameter
-        return squeeze(axis=axis)
-    except TypeError:
-        # For backwards compatibility
+    if axis is None:
         return squeeze()
-
+    else:
+        return squeeze(axis=axis)
 
 def diagonal(a, offset=0, axis1=0, axis2=1):
     """
diff --git a/numpy/core/tests/test_regression.py b/numpy/core/tests/test_regression.py
index 016b720f3..119594668 100644
--- a/numpy/core/tests/test_regression.py
+++ b/numpy/core/tests/test_regression.py
@@ -1675,6 +1675,67 @@ class TestRegression(object):
         assert_(a.flags.f_contiguous)
         assert_(b.flags.f_contiguous)
 
+    def test_squeeze_axis_handling(self):
+        # Issue #10779
+        # Ensure proper handling of objects
+        # that don't support axis specification
+        # when squeezing
+
+        class OldSqueeze(np.ndarray):
+
+            def __new__(cls,
+                        input_array):
+                obj = np.asarray(input_array).view(cls)
+                return obj
+
+            # it is perfectly reasonable that prior
+            # to numpy version 1.7.0 a subclass of ndarray
+            # might have been created that did not expect
+            # squeeze to have an axis argument
+            # NOTE: this example is somewhat artificial;
+            # it is designed to simulate an old API
+            # expectation to guard against regression
+            def squeeze(self):
+                return super(OldSqueeze, self).squeeze()
+
+        oldsqueeze = OldSqueeze(np.array([[1],[2],[3]]))
+
+        # if no axis argument is specified the old API
+        # expectation should give the correct result
+        assert_equal(np.squeeze(oldsqueeze),
+                     np.array([1,2,3]))
+
+        # likewise, axis=None should work perfectly well
+        # with the old API expectation
+        assert_equal(np.squeeze(oldsqueeze, axis=None),
+                     np.array([1,2,3]))
+
+        # however, specification of any particular axis
+        # should raise a TypeError in the context of the
+        # old API specification, even when using a valid
+        # axis specification like 1 for this array
+        with assert_raises(TypeError):
+            # this would silently succeed for array
+            # subclasses / objects that did not support
+            # squeeze axis argument handling before fixing
+            # Issue #10779
+            np.squeeze(oldsqueeze, axis=1)
+
+        # check for the same behavior when using an invalid
+        # axis specification -- in this case axis=0 does not
+        # have size 1, but the priority should be to raise
+        # a TypeError for the axis argument and NOT a
+        # ValueError for squeezing a non-empty dimension
+        with assert_raises(TypeError):
+            np.squeeze(oldsqueeze, axis=0)
+
+        # the new API knows how to handle the axis
+        # argument and will return a ValueError if
+        # attempting to squeeze an axis that is not
+        # of length 1
+        with assert_raises(ValueError):
+            np.squeeze(np.array([[1],[2],[3]]), axis=0)
+
     def test_reduce_contiguous(self):
         # GitHub issue #387
         a = np.add.reduce(np.zeros((2, 1, 2)), (0, 1))