[GitHub] [beam] lostluck commented on a change in pull request #12426: [BEAM-7996] Add support for MapType and Nulls in container types for Python RowCoder

[GitBox <gi...@apache.org>]

lostluck commented on a change in pull request #12426:
URL: https://github.com/apache/beam/pull/12426#discussion_r464647966



##########
File path: sdks/python/apache_beam/coders/coder_impl.py
##########
@@ -530,6 +530,88 @@ def estimate_size(self, unused_value, nested=False):
     return 1
 
 
+class MapCoderImpl(StreamCoderImpl):
+  """For internal use only; no backwards-compatibility guarantees.
+
+  A coder for typing.Mapping objects."""
+  def __init__(
+      self,
+      key_coder,  # type: CoderImpl
+      value_coder  # type: CoderImpl
+  ):
+    self._key_coder = key_coder
+    self._value_coder = value_coder
+
+  def encode_to_stream(self, value, out, nested):
+    size = len(value)
+    out.write_bigendian_int32(size)

Review comment:
       As a practical matter, int32 max of any amount of data is bigger than our GRPC limits for receiving single values into an SDK. At least, until we add a large value protocol to stream in single large values somewhere.




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