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Diffstat (limited to 'tensorflow/contrib/autograph/converters/list_comprehensions.py')
-rw-r--r-- | tensorflow/contrib/autograph/converters/list_comprehensions.py | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/tensorflow/contrib/autograph/converters/list_comprehensions.py b/tensorflow/contrib/autograph/converters/list_comprehensions.py new file mode 100644 index 0000000000..ecf4628816 --- /dev/null +++ b/tensorflow/contrib/autograph/converters/list_comprehensions.py @@ -0,0 +1,82 @@ +# 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. +# ============================================================================== +"""Lowers list comprehensions into for and if statements. + +Example: + + result = [x * x for x in xs] + +becomes + + result = [] + for x in xs: + elt = x * x + result.append(elt) +""" + +from __future__ import absolute_import +from __future__ import division +from __future__ import print_function + +import gast + +from tensorflow.contrib.autograph.core import converter +from tensorflow.contrib.autograph.pyct import templates + + +# TODO(mdan): This should covert directly to operator calls. + + +class ListCompTransformer(converter.Base): + """Lowers list comprehensions into standard control flow.""" + + def visit_Assign(self, node): + if not isinstance(node.value, gast.ListComp): + return self.generic_visit(node) + if len(node.targets) > 1: + raise NotImplementedError('multiple assignments') + + target, = node.targets + list_comp_node = node.value + + template = """ + target = [] + """ + initialization = templates.replace(template, target=target) + + template = """ + target.append(elt) + """ + body = templates.replace(template, target=target, elt=list_comp_node.elt) + + for gen in reversed(list_comp_node.generators): + for gen_if in reversed(gen.ifs): + template = """ + if test: + body + """ + body = templates.replace(template, test=gen_if, body=body) + template = """ + for target in iter_: + body + """ + body = templates.replace( + template, iter_=gen.iter, target=gen.target, body=body) + + return initialization + body + + +def transform(node, ctx): + return ListCompTransformer(ctx).visit(node) |