Passing Protocol buffer serialized datas from C++ to Python via LevelDB - c++

Question

Though I've followed the excellent Protocol Buffer documentation and tutorials for C++ and Python, I can't achieve my goal which is :
- to serialize datas from a C++ process.
- insert it into LevelDB from that same process.
- extract the serialized datas from a Python process
- Deseralize it from this same Python process
- Use those deseralized datas in Python
I can serialize my datas using protocol buffer in C++ (using a std::string container). I can insert it into LevelDB. But, when I levelDB->Get my serialized datas, though Python seems to recognize it as a String, and showing me their raw content, whenever I deserialize it into a Python String, it is empty!
Here is how I serialize and insert my datas in C++ :
int main(int arg, char** argv)
{
GOOGLE_PROTOBUF_VERIFY_VERSION;
leveldb::DB* db;
leveldb::Options options;
leveldb::Status status;
tutorial::AddressBook address_book;
tutorial::Person* person1;
tutorial::Person* person2;
options.create_if_missing = true;
status = leveldb::DB::Open(options, "test_db", &db);
assert(status.ok());
person1 = address_book.add_person();
person1->set_id(1);
person1->set_name("ME");
person1->set_email("me#me.com");
person2 = address_book.add_person();
person2->set_id(2);
person2->set_name("SHE");
person2->set_email("she#she.com");
std::string test;
if (!address_book.SerializeToString(&test))
{
std::cerr << "Failed to write address book" << std::endl;
return -1;
}
if (status.ok()) status = db->Put(leveldb::WriteOptions(), "Test", test);
And here is how I try to deserialize it in Python:
address_book = addressbook_pb2.AddressBook()
db = leveldb.LevelDB('test_db')
ab = address_book.ParseFromString(db.Get("Test"))
ad var type is NoneType
Edit :
before the db.Get(), ab.ByteSize() returns 0, 76 after the ParseFromString(), I assume it's a Type problem then...
+
ab.ListFields() returns a unexploitable list of the contained field: succesfully couting two person instances, but unable to let me acces to it.
Any clues, any ideas of what I didn't understand, what I'm doing wrong here?
Many thanks!

Answer 1

Ok, so this was my bad.
I went back into the Protocol Buffers Python documentation, and the fact is that even if the AdressBook object I was retrieving did not showed any description, it was still able to be iterated over and even had a .str() method.
so, if anyone comes to that problem again, just try to explore your ProtocolBuffers object using iPython like I did, and you'll find that every of your proto elements are fields of your object.
Using my example:
ab = adress_book.ParseFromString(db.Get('Test'))
ab.__str__() # Shows a readable version of my object
for person in adress_book.person: # I'm even able to iterate over any of my ab fields values
print person.id
print person.name

Answer 2

Try using ' instead of ":
ab = address_book.ParseFromString(db->Get('Test'))