liferoad commented on code in PR #26059: URL: https://github.com/apache/beam/pull/26059#discussion_r1218153677
########## sdks/python/apache_beam/coders/union_coder.py: ########## @@ -0,0 +1,123 @@ +# +# Licensed to the Apache Software Foundation (ASF) under one or more +# contributor license agreements. See the NOTICE file distributed with +# this work for additional information regarding copyright ownership. +# The ASF licenses this file to You 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. +# + +# pytype: skip-file + +import struct + +from typing import Iterable +from typing import List +from typing import Tuple + +from apache_beam.coders import Coder +from apache_beam.coders.coders import FastCoder +from apache_beam.typehints import typehints + + +class UnionCoder(FastCoder): + def __init__(self, components): + # type: (Iterable[Coder]) -> None + if not components or not isinstance(components, list): + raise ValueError('A valid list of Coders must be provided.') + + if len(components) > 255 or len(components) <= 1: + raise ValueError( + 'The number of components for UnionCoder must be between 2 and 255.') + + self._coders = components + self._coder_typehints = {} + for i, c in enumerate(self._coders): + type_hint = c.to_type_hint() + if type_hint in self._coder_typehints: + raise ValueError( + f'One coder {self._coder_typehints.get(type_hint)} already ' + f'exists for this type {type_hint}.') + else: + self._coder_typehints[type_hint] = (struct.pack("B", i), c) + + def _get_coder(self, value) -> Tuple[bytes, Coder]: + # have to linearly scan the typehints since type could be composite + # simple type(value) does not work + typehint_type = None + for th in self._coder_typehints: + try: + typehints.check_constraint(th, value) + typehint_type = th + break + except (typehints.CompositeTypeHintError, typehints.SimpleTypeHintError): + pass + except Exception as e: + raise ValueError( + f"cannot check the value {value} type and the error is {e}") + + if typehint_type in self._coder_typehints: + return self._coder_typehints.get(typehint_type) + raise ValueError( + 'Could not find a matching component coder ' + 'in the coder {} to encode a value {} with a typehint {}.'.format( + self, value, typehint_type)) + + def encode(self, value) -> bytes: + """ + Encodes the given Union value into bytes. + """ + coder_tag, real_coder = self._get_coder(value) + return coder_tag + real_coder.encode(value) + + def decode(self, encoded: bytes): + """ + Decodes the given bytes into a Union value. + """ + try: + coder_index = struct.unpack("B", encoded[:1])[0] + coder = self._coders[coder_index] + + return coder.decode(encoded[1:]) + except Exception: # pylint: disable=broad-except + raise ValueError(f'cannot decode {encoded} with the coder {self}') Review Comment: I think this is not needed for f-string. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
