From 200d57c77da07d620960f16f1b4fba3865d868e3 Mon Sep 17 00:00:00 2001
From: liym27 <33742067+liym27@users.noreply.github.com>
Date: Thu, 3 Jun 2021 10:49:14 +0800
Subject: [PATCH] [getitem] Support index is None for getitem in static mode
 (#33001)

---
 .../fluid/tests/unittests/test_variable.py    | 56 +++++++++++++++++++
 python/paddle/fluid/variable_index.py         | 49 ++++++++++++++--
 2 files changed, 101 insertions(+), 4 deletions(-)

diff --git a/python/paddle/fluid/tests/unittests/test_variable.py b/python/paddle/fluid/tests/unittests/test_variable.py
index 6b99e855917..6ffecd33f8f 100644
--- a/python/paddle/fluid/tests/unittests/test_variable.py
+++ b/python/paddle/fluid/tests/unittests/test_variable.py
@@ -295,5 +295,61 @@ class TestVariable(unittest.TestCase):
         self.assertRaises(Exception, _test)
 
 
+class TestVariableSlice(unittest.TestCase):
+    def _test_item_none(self, place):
+        data = np.random.rand(2, 3, 4).astype("float32")
+        prog = paddle.static.Program()
+        with paddle.static.program_guard(prog):
+            x = paddle.assign(data)
+            out0 = x[0:, None, 1:]
+            out1 = x[0:, None]
+            out2 = x[None, 1:]
+            out3 = x[None]
+
+        outs = [out0, out1, out2, out3]
+        exe = paddle.static.Executor(place)
+        result = exe.run(prog, fetch_list=outs)
+
+        expected = [
+            data[0:, None, 1:], data[0:, None], data[None, 1:], data[None]
+        ]
+        for i in range(len(outs)):
+            self.assertEqual(outs[i].shape, expected[i].shape)
+            self.assertTrue((result[i] == expected[i]).all())
+
+    def _test_item_none_and_decrease(self, place):
+        data = np.random.rand(2, 3, 4).astype("float32")
+        prog = paddle.static.Program()
+        with paddle.static.program_guard(prog):
+            x = paddle.assign(data)
+            out0 = x[0, 1:, None]
+            out1 = x[0, None]
+            out2 = x[None, 1]
+            out3 = x[None]
+            out4 = x[0, 0, 0, None]
+            out5 = x[None, 0, 0, 0, None]
+
+        outs = [out0, out1, out2, out3, out4, out5]
+        exe = paddle.static.Executor(place)
+        result = exe.run(prog, fetch_list=outs)
+        expected = [
+            data[0, 1:, None], data[0, None], data[None, 1], data[None],
+            data[0, 0, 0, None], data[None, 0, 0, 0, None]
+        ]
+
+        for i in range(len(outs)):
+            self.assertEqual(outs[i].shape, expected[i].shape)
+            self.assertTrue((result[i] == expected[i]).all())
+
+    def test_slice(self):
+        places = [fluid.CPUPlace()]
+        if core.is_compiled_with_cuda():
+            places.append(core.CUDAPlace(0))
+
+        for place in places:
+            self._test_item_none(place)
+            self._test_item_none_and_decrease(place)
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/python/paddle/fluid/variable_index.py b/python/paddle/fluid/variable_index.py
index 31545a84004..aed8c82d43b 100644
--- a/python/paddle/fluid/variable_index.py
+++ b/python/paddle/fluid/variable_index.py
@@ -50,6 +50,17 @@ def replace_ellipsis(var, item):
     return item
 
 
+def replace_none(item):
+    new_item = []
+    none_axes = []
+    for i, slice_item in enumerate(item):
+        if slice_item is None:
+            none_axes.append(i)
+        else:
+            new_item.append(slice_item)
+    return new_item, none_axes
+
+
 def is_integer_or_scalar_tensor(ele):
     from .framework import Variable
     if isinstance(ele, int):
@@ -97,9 +108,10 @@ def _getitem_impl_(var, item):
     starts = []
     ends = []
     steps = []
-    reverse_axis = []
+    reverse_axes = []
 
     use_strided_slice = False
+    item, none_axes = replace_none(item)
 
     for dim, slice_item in enumerate(item):
         if is_integer_or_scalar_tensor(slice_item):
@@ -120,7 +132,7 @@ def _getitem_impl_(var, item):
 
             if start is None and end is None:
                 assert (step == -1)
-                reverse_axis.append(dim)
+                reverse_axes.append(dim)
                 continue
 
             start = 0 if start is None else start
@@ -195,9 +207,38 @@ def _getitem_impl_(var, item):
             attrs=attrs)
         out = slice_out_var
 
-    if len(reverse_axis) > 0:
+    if len(reverse_axes) > 0:
         from .layers.tensor import reverse
-        out = reverse(out, axis=reverse_axis)
+        out = reverse(out, axis=reverse_axes)
+
+    # Deal with cases when all axes are decreased.
+    # After slice, the shape of out is [1], which should have been [], but Paddle doesn't support scalar.
+    # In order to ensure the correctness of the final shape of out, one dimension of out needs to be decreased.
+    # For example:
+    # # x.shape: (2,3,4)
+    # out = x[0, 1, 1, None] # out.shape : (1)
+    if len(decrease_axes) == len(var.shape):
+        none_axes = none_axes[1:]
+
+    if len(none_axes) > 0:
+        # Deal with cases that decrease_axes is not empty
+        # For example:
+        # # x.shape: (2,3,4)
+        # out = x[0, 0:2, None] # out.shape : (2, 1, 4)
+        for idx, axis in enumerate(none_axes):
+            l = len([i for i in decrease_axes if i < axis])
+            new_axis = axis - l
+            none_axes[idx] = new_axis
+
+        # Deal with cases when all axes are decreased.
+        # After slice, the shape of out is [1], which should have been [], but Paddle doesn't support scalar.
+        # In order to ensure the correctness of the final shape of out, one dimension of out needs to be decreased.
+        # For example:
+        # # x.shape: (2,3,4)
+        # out = x[0, 1, 1, None] # out.shape : (1)
+
+        from ..tensor import unsqueeze
+        out = unsqueeze(out, axis=none_axes)
 
     return out
 
-- 
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