[GitHub] [beam] tvalentyn commented on a diff in pull request #26059: Add a simple UnionCoder

["tvalentyn (via GitHub)" <gi...@apache.org>]

tvalentyn commented on code in PR #26059:
URL: https://github.com/apache/beam/pull/26059#discussion_r1175189637


##########
sdks/python/apache_beam/coders/union_coder.py:
##########
@@ -0,0 +1,94 @@
+#
+# 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, List
+
+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 = {
+        c.to_type_hint(): (struct.pack("B", i), c)
+        for i,
+        c in enumerate(self._coders)
+    }
+
+  def encode(self, value) -> bytes:
+    """
+        Encodes the given Union value into bytes.
+        """
+    typehint_type = type(value)
+    coder_t = self._coder_typehints.get(typehint_type, None)
+    if coder_t:

Review Comment:
   for readability, let's unpack coder_t into two variables so that coder_t[0] and coder_t[1] are referred to by some mnemonic names.



##########
sdks/python/apache_beam/coders/union_coder.py:
##########
@@ -0,0 +1,94 @@
+#
+# 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, List
+
+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 = {
+        c.to_type_hint(): (struct.pack("B", i), c)
+        for i,
+        c in enumerate(self._coders)
+    }
+
+  def encode(self, value) -> bytes:
+    """
+        Encodes the given Union value into bytes.
+        """
+    typehint_type = type(value)
+    coder_t = self._coder_typehints.get(typehint_type, None)
+    if coder_t:
+      return coder_t[0] + coder_t[1].encode(value)
+    else:
+      raise ValueError(
+          "Unknown type {} for UnionCoder with the value {}. ".format(

Review Comment:
   I think it may be good to include components of our UnionCoder in the message.



##########
sdks/python/apache_beam/coders/union_coder.py:
##########
@@ -0,0 +1,94 @@
+#
+# 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, List
+
+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 = {
+        c.to_type_hint(): (struct.pack("B", i), c)
+        for i,
+        c in enumerate(self._coders)
+    }
+
+  def encode(self, value) -> bytes:
+    """
+        Encodes the given Union value into bytes.
+        """
+    typehint_type = type(value)
+    coder_t = self._coder_typehints.get(typehint_type, None)
+    if coder_t:
+      return coder_t[0] + coder_t[1].encode(value)
+    else:
+      raise ValueError(
+          "Unknown type {} for UnionCoder with the value {}. ".format(
+              typehint_type, 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}")
+
+  def is_deterministic(self) -> bool:
+    """
+        Returns True if all sub-coders are deterministic.
+        """
+    return all(c.is_deterministic() for c in self._coders)
+
+  def to_type_hint(self) -> typehints.UnionConstraint:
+    """
+        Returns a type hint representing the Union type with the sub-coders.
+        """
+    return typehints.Union[list(self._coder_typehints.keys())]
+
+  def coders(self):
+    # type: () -> List[Coder]
+    return self._coders
+
+  def __eq__(self, other):
+    return type(self) == type(other) and self._coders == other.coders()
+
+  def __repr__(self) -> str:

Review Comment:
   re more APIs: 
   
   1. you inherit from FastCoder. My understanding is FastCoder coders are expected to provide an impl, which will be Cython-translated into C code and then compiled, which will make the implementation fast, as opposed to slow Python implementation.  see: https://github.com/apache/beam/blob/f549fd33abdc672143ccbe3f0f66104995d30fe6/sdks/python/apache_beam/coders/coders.py#L465, https://github.com/apache/beam/blob/master/sdks/python/apache_beam/coders/coder_impl.py. 
   
   I see that this coder doesn't provide an impl, which may be an issue as it may invalidate assumptions about what a FastCoder is.
   
   2. I see that TupleCoder has a registered URN, we might need to do the same.
   
   re hash: I think right now default hash implementation definded in `Coder.hash` will be used. Sounds like we could repeat `Tuple.__hash__ ()` here.



##########
sdks/python/apache_beam/coders/union_coder.py:
##########
@@ -0,0 +1,94 @@
+#
+# 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, List
+
+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 = {
+        c.to_type_hint(): (struct.pack("B", i), c)
+        for i,
+        c in enumerate(self._coders)
+    }
+
+  def encode(self, value) -> bytes:
+    """
+        Encodes the given Union value into bytes.
+        """
+    typehint_type = type(value)
+    coder_t = self._coder_typehints.get(typehint_type, None)
+    if coder_t:
+      return coder_t[0] + coder_t[1].encode(value)
+    else:
+      raise ValueError(
+          "Unknown type {} for UnionCoder with the value {}. ".format(
+              typehint_type, 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}")

Review Comment:
   Likewise here we could be more detailed about what Union coder we had and which coder_index or coder (beware of potential IndexError) we attempted to use. 



##########
sdks/python/apache_beam/coders/union_coder_test.py:
##########
@@ -0,0 +1,75 @@
+#
+# 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 logging
+import unittest
+
+from apache_beam.coders import coders
+from apache_beam.coders.union_coder import UnionCoder
+from apache_beam.coders.avro_record import AvroRecord
+
+
+class AvroTestCoder(coders.AvroGenericCoder):
+  SCHEMA = """
+  {
+    "type": "record", "name": "test",
+    "fields": [
+      {"name": "name", "type": "string"},
+      {"name": "age", "type": "int"}
+    ]
+  }
+  """
+
+  def __init__(self):
+    super().__init__(self.SCHEMA)
+
+
+class UnionCoderTest(unittest.TestCase):
+  def test_basics(self):
+    coder_0 = UnionCoder([
+        coders.StrUtf8Coder(),
+        coders.VarIntCoder(),
+    ])
+    coder = UnionCoder([
+        coders.StrUtf8Coder(),
+        coders.VarIntCoder(),
+        coders.FloatCoder(),
+    ])
+    assert coder != coder_0
+    for v in ["8", 8, 8.0]:
+      self.assertEqual(v, coder.decode(coder.encode(v)))
+
+  def test_custom_coder(self):
+
+    coder = UnionCoder([AvroTestCoder(), coders.BooleanCoder()])
+
+    self.assertEqual(coder.is_deterministic(), False)
+
+    assert coder.to_type_hint()
+    assert str(coder) == 'UnionCoder[AvroTestCoder, BooleanCoder]'
+
+    ar = AvroRecord({"name": "Daenerys targaryen", "age": 23})
+    self.assertEqual(coder.decode(coder.encode(ar)).record, ar.record)
+
+    for v in [True]:

Review Comment:
   just checking if you meant to have more than 1 value here



##########
sdks/python/apache_beam/coders/union_coder.py:
##########
@@ -0,0 +1,94 @@
+#
+# 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, List
+
+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 = {
+        c.to_type_hint(): (struct.pack("B", i), c)
+        for i,
+        c in enumerate(self._coders)
+    }
+
+  def encode(self, value) -> bytes:
+    """
+        Encodes the given Union value into bytes.
+        """
+    typehint_type = type(value)
+    coder_t = self._coder_typehints.get(typehint_type, None)
+    if coder_t:
+      return coder_t[0] + coder_t[1].encode(value)
+    else:
+      raise ValueError(
+          "Unknown type {} for UnionCoder with the value {}. ".format(

Review Comment:
   Consider following wording:
   Couldn't find a matching component coder in the Union[...] coder to encode a value with a typehint xyz. 



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