AttributeError: Assignment not allowed to composite field "task" in protocol message object

Question

I'm using protocol-buffers python lib to send data,but it's have some problems, so

Traceback (most recent call last):
  File "test_message.py", line 17, in <module>
    ptask.task = task
  File "build\bdist.win32\egg\google\protobuf\internal\python_message.py", line
513, in setter
AttributeError: Assignment not allowed to composite field "_task" in protocol message object.

the src as follows:

proto file:

message task {
    required int32 id = 1;
    required string msg = 2;
}

message task_info {
    required task task = 1;
}

python code:

task = yacc.task()
task.id = 1000
task.msg = u"test"
ptask = yacc.task_info() 
ptask.task = task # this line happen the runtime error

John McFarlane · Accepted Answer · 2020-03-01 02:39:45Z

145

Try CopyFrom:

ptask.task.CopyFrom(task)

edited Mar 1, 2020 at 2:39

answered Mar 31, 2014 at 20:33

John McFarlane

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2 Comments

John McFarlane Over a year ago

@Cu2S golden rule of StackExchange: always at least read the first two answers!

Ferran Maylinch Over a year ago

This is THE answer. The MergeFrom mentioned in other answers can also be useful sometimes.

Martin Maillard · Accepted Answer · 2013-08-22 09:28:49Z

48

I don't know protocol-buffers but I took a look at the docs and it says:

You cannot assign a value to an embedded message field. Instead, assigning a value to any field within the child message implies setting the message field in the parent.

So I'm assuming this should work:

task = yacc.task()
task.id = 1000
task.msg = u"test"
ptask = yacc.task_info() 
ptask.task.id = task.id
ptask.task.msg = task.msg

answered Aug 22, 2013 at 9:28

Martin Maillard

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1 Comment

Ferran Maylinch Over a year ago

This is the section of the docs where it talks about that. It also mentions the CopyFrom method.

Aleksandro M Granda · Accepted Answer · 2013-12-27 21:59:25Z

23

I'm new to protocol-buffers too and faced with the same problem. I've found this method helpful.

I think it should work:

task = yacc.task()
task.id = 1000
task.msg = u"test"
ptask = yacc.task_info() 
ptask.task.MergeFrom(task)

answered Dec 27, 2013 at 21:59

Aleksandro M Granda

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1 Comment

Mark Parris Over a year ago

CopyFrom() calls MergeFrom() after Clearing the object

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