Add py api for sequence_slice_op

test=develop

paddle/fluid/platform/profiler.cc

@@ -370,8 +370,8 @@ void ParseEvents(const std::vector<std::vector<Event>>& events,
   std::vector<std::vector<Event>> merged_events_list;
   if (merge_thread) {
     std::vector<Event> merged_events;
-    for (int i = 0; i < events.size(); ++i) {
-      for (int j = 0; j < events[i].size(); ++j) {
+    for (size_t i = 0; i < events.size(); ++i) {
+      for (size_t j = 0; j < events[i].size(); ++j) {
         merged_events.push_back(events[i][j]);
       }
     }

python/paddle/fluid/layers/nn.py

@@ -64,6 +64,7 @@ __all__ = [
     'reduce_prod',
     'sequence_first_step',
     'sequence_last_step',
+    'sequence_slice',
     'dropout',
     'split',
     'ctc_greedy_decoder',
@@ -1901,6 +1902,72 @@ def sequence_last_step(input):
     return sequence_pool(input=input, pool_type="last")
 
 
+def sequence_slice(input, offset, length, name=None):
+    """
+    **Sequence Slice Layer**
+
+    The layer crops a subsequence from given sequence with given start 
+    offset and subsequence length.
+
+    It only supports sequence data (LoDTensor with lod_level equal to 1).
+
+    .. code-block:: text
+    
+	- Case:
+            Given the input Variable **input**,
+	        input.data = [[a1, a2], [b1, b2], [c1, c2], [d1, d2], [e1, e2]],
+	        input.lod = [[0, 3, 5]], input.dims = (5, 2)
+
+	    with offset.data = [[0], [1]], length.data = [[2], [1]],
+
+            the output Variable will be
+
+	        out.data = [[a1, a2], [b1, b2], [e1, e2]],
+	        out.lod = [[0, 2, 3]], out.dims = (3, 2)
+	
+    NOTE: The first dimension size of input, the size of offset and Length, 
+          should be equal. The offset start from 0.
+    
+    Args:
+        input(Variable): The input Variable which consists of the complete 
+                         sentences.
+        offset(Variable): The offset to slice each sequence.
+        length(Variable): The length of each subsequence.
+        name(str|None): A name for this layer(optional). If set None, the
+                        layer will be named automatically.
+
+    Returns:
+        Variable: The subsequences.
+
+    Examples:
+
+        .. code-block:: python
+
+             import numpy as np
+             seqs = fluid.layers.data(name='x', shape=[10, 5],
+                              dtype='float32', lod_level=1)
+             offset = fluid.layers.assign(input=np.array([[0, 1]]).astype("int32"))
+             length = fluid.layers.assign(input=np.array([[2, 1]]).astype("int32"))
+             subseqs = fluid.layers.sequence_slice(input=seqs, offset=offset, 
+                                                   length=length)
+    """
+    helper = LayerHelper("sequence_slice", **locals())
+    dtype = helper.input_dtype()
+    out = helper.create_tmp_variable(dtype)
+
+    offset.stop_gradient = True
+    length.stop_gradient = True
+
+    helper.append_op(
+        type="sequence_slice",
+        inputs={"X": input,
+                "Offset": offset,
+                "Length": length},
+        outputs={"Out": out})
+
+    return out
+
+
 @templatedoc()
 def pool2d(input,
            pool_size=-1,

python/paddle/fluid/tests/unittests/test_layers.py

@@ -406,6 +406,19 @@ class TestBook(unittest.TestCase):
             self.assertIsNotNone(out)
         print(str(program))
 
+    def test_sequence_slice(self):
+        program = Program()
+        with program_guard(program):
+            import numpy as np
+            seqs = layers.data(
+                name='x', shape=[10, 5], dtype='float32', lod_level=1)
+            offset = layers.assign(input=np.array([[0, 1]]).astype('int32'))
+            length = layers.assign(input=np.array([[2, 1]]).astype('int32'))
+            out = layers.sequence_slice(
+                input=seqs, offset=offset, length=length)
+            self.assertIsNotNone(out)
+        print(str(program))
+
     def test_lod_reset(self):
         program = Program()
         with program_guard(program):