while deserialising the protobuf as per .proto value is empty string - protocol-buffers

Question

protobuf:
message test
{
int16 a:1
message testdata{
int16 b:1 `
int16 c:2
repeated testdata test_data=2
}
}
dt=test()
dt.a=11
dt1=d.testdata.add()
dt1.b=2222
dt1.c=3333
send=dt.SerializeToString()
now while deserialising code as below:
t=test()
t.ParseFromString(send)
t1=t.testdata()
print(t1.test_data)----> empty string
print(t1.b)--> value is not printing as expected, its printing object name instead of value.
how to access the nested protobuf elements and any input or suggestions are welcome.

Answer 1

I encourage you to read the documentation.
Your protobuf file is invalid.
A working equivalent of what you've written could be:
example.proto:
syntax = "proto3";
message test {
int32 a=1;
message testdata {
int32 b=1;
int32 c=2;
}
repeated testdata test_data=2;
}
Compiled using:
protoc \
--proto_path=${PWD} \
--python_out=${PWD} \
${PWD}/example.proto
Example Python code (with apologies for my poor variable naming choices):
import example_pb2
from google.protobuf.message import DecodeError
# Create a test message (f)
f = example_pb2.test()
f.a = 1
# Add a repeated property of type testdata
g=f.test_data.add()
g.b=1
g.c=1
# Add a repeated property of type testdata
g=f.test_data.add()
g.b=2
g.c=2
# Add a repeated property of type testdata
g=f.test_data.add()
g.b=3
g.c=3
# Output it
print(f)
# Serialize it and output it
x=f.SerializeToString()
print(x)
# Create a new test message (h) and parse x into it
h=example_pb2.test()
h.ParseFromString(x)
print(h)
# Create incorrectly formatted message (y) as a variant of x
y=b'\x08\x01\x12\x12\x04\x08\x01\x10\x01\x12\x04\x08\x02\x10\x02\x12\x04\x08\x03\x10\x03'
j=example_pb2.test()
try:
j.ParseFromString(y)
print(j)
except DecodeError as e:
print(e)
Yielding:
a: 1
test_data {
b: 1
c: 1
}
test_data {
b: 2
c: 2
}
test_data {
b: 3
c: 3
}
b'\x08\x01\x12\x04\x08\x01\x10\x01\x12\x04\x08\x02\x10\x02\x12\x04\x08\x03\x10\x03'
a: 1
test_data {
b: 1
c: 1
}
test_data {
b: 2
c: 2
}
test_data {
b: 3
c: 3
}
Error parsing message