79 lines
2.1 KiB
Python
79 lines
2.1 KiB
Python
# Copyright 2016 The TensorFlow Authors. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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# ==============================================================================
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"""Lowers list comprehensions into for and if statements.
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Example:
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result = [x * x for x in xs]
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becomes
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result = []
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for x in xs:
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elt = x * x
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result.append(elt)
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"""
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import gast
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from tensorflow.python.autograph.core import converter
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from tensorflow.python.autograph.pyct import templates
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# TODO(mdan): This should covert directly to operator calls.
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class ListCompTransformer(converter.Base):
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"""Lowers list comprehensions into standard control flow."""
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def visit_Assign(self, node):
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if not isinstance(node.value, gast.ListComp):
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return self.generic_visit(node)
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if len(node.targets) > 1:
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raise NotImplementedError('multiple assignments')
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target, = node.targets
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list_comp_node = node.value
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template = """
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target = []
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"""
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initialization = templates.replace(template, target=target)
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template = """
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target.append(elt)
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"""
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body = templates.replace(template, target=target, elt=list_comp_node.elt)
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for gen in reversed(list_comp_node.generators):
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for gen_if in reversed(gen.ifs):
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template = """
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if test:
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body
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"""
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body = templates.replace(template, test=gen_if, body=body)
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template = """
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for target in iter_:
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body
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"""
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body = templates.replace(
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template, iter_=gen.iter, target=gen.target, body=body)
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return initialization + body
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def transform(node, ctx):
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return ListCompTransformer(ctx).visit(node)
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