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+# Copyright 2016 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Converter for slice operations."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import gast
+
+from tensorflow.python.autograph.core import converter
+from tensorflow.python.autograph.lang import directives
+from tensorflow.python.autograph.pyct import templates
+
+
+class SliceTransformer(converter.Base):
+ """Converts slicing operations to their TF counterpart.
+
+ Currently, relying on the default slice operator that Tensor uses is
+ insufficient, because TensorArray and tensor lists use dedicated index read
+ and write functions.
+ """
+
+ def _process_single_assignment(self, target, value):
+ if not isinstance(target, gast.Subscript):
+ return None
+ if not isinstance(target.slice, gast.Index):
+ return None
+
+ template = """
+ target = ag__.set_item(target, key, item)
+ """
+ return templates.replace(
+ template, target=target.value, key=target.slice.value, item=value)
+
+ def visit_Assign(self, node):
+ node = self.generic_visit(node)
+ # TODO(mdan): Support unpackings and multiple assignments.
+ if len(node.targets) != 1:
+ raise NotImplementedError('multiple assignment')
+ replacement = self._process_single_assignment(node.targets[0], node.value)
+ if replacement is not None:
+ return replacement
+ return node
+
+ def visit_Subscript(self, node):
+ node = self.generic_visit(node)
+ if not isinstance(node.slice, gast.Index):
+ return node
+
+ if not isinstance(node.ctx, gast.Load):
+ # Index writes are handled at a higher level, one at which the rvalue is
+ # also available.
+ return node
+
+ dtype = self.get_definition_directive(
+ node.value,
+ directives.set_element_type,
+ 'dtype',
+ default=templates.replace_as_expression('None'))
+
+ template = """
+ ag__.get_item(
+ target,
+ key,
+ opts=ag__.GetItemOpts(element_dtype=dtype))
+ """
+ return templates.replace_as_expression(
+ template, target=node.value, key=node.slice.value, dtype=dtype)
+
+
+def transform(node, ctx):
+ return SliceTransformer(ctx).visit(node)