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

问题

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 

回答1:

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

回答2:

Try CopyFrom:

ptask.task.CopyFrom(task)

回答3:

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)

来源：https://stackoverflow.com/questions/18376190/attributeerror-assignment-not-allowed-to-composite-field-task-in-protocol-mes