Hi Mike,

Python indeed has descriptor classes that you can use to build proto 
definitions at runtime. However it does not have a parser for .proto files 
built in. So if you want to load .proto files at runtime, you'll need to 
use protoc to build a descriptor (for example, you could shell out to 


On Monday, March 21, 2016 at 10:43:24 AM UTC-7, Mike Trienis wrote:
> Hi,
> Do you know if it's possible do dynamic decoding at run-time using the 
> Python API? 
>    - https://developers.google.com/protocol-buffers/docs/reference/python/
> Indeed there is a descriptor.FileDescriptor, however I'm not sure what the 
> other classes correspond to?
> Thanks, Mike. 
> On Tuesday, August 12, 2014 at 10:36:13 AM UTC-7, Feng Xiao wrote:
>> Protobuf supports creating message types dynamically at runtime and use 
>> them for parsing/serialization/etc.
>> First you need to build up a DescriptorPool 
>> <https://code.google.com/p/protobuf/source/browse/trunk/src/google/protobuf/descriptor.h#1141>
>> that contains all types that you may want to use. There are two approaches 
>> to construct this pool. One is to call DescriptorPool::BuildFile() directly 
>> with parsed proto files. For example:
>>   // Convert .proto files into parsed FileDescriptorProto
>>   bool ParseProtoFile(string filename, FileDescriptorProto* result) {
>>     FileInputStream stream(filename);
>>     google::protobuf::io::Tokenizer tokenizer(&stream);
>>     google::protobuf::compiler::Parser parser;
>>     return parser.Parse(&tokenizer, result);
>>   }
>>   // Build the descriptor pool
>>   DescriptorPool pool;
>>   for (string filename : proto_files) {
>>     FileDescriptorProto proto;
>>     ParseProtoFile(filename, &proto);
>>     pool.BuildFile(proto);
>>   }
>> After you have the pool, you can query for a type by its name. For 
>> example, DescriptorPool::FindMessageTypeByName().
>> Then to actually parse/serialize/use message types in the pool, you need 
>> to construct message objects around them. DynamicMessage 
>> <https://code.google.com/p/protobuf/source/browse/trunk/src/google/protobuf/dynamic_message.h#53>
>> is used for that:
>>   // Suppose you want to parse a message type with a specific type name.
>>   Descriptor* descriptor = 
>> pool.FindMessageTypeByName(message_type_to_parse);
>>   DynamicMessageFactory factory;
>>   unique_ptr<Message> message = factory.GetPrototype(descriptor)->New();
>>   // Use the message object for parsing/etc.
>>   message->ParseFromString(input_data);
>>   // Access a specific field in the message
>>   FieldDescriptor* field = descriptor->FindFieldByName(field_to_read);
>>   switch (field->type()) {
>>     case TYPE_INT32: message->GetReflection()->GetInt32(*message, field); 
>> break;
>>     ...
>>   }
>> On Mon, Aug 11, 2014 at 9:31 PM, Jan Kyjovský <jan.ky...@tieto.com> 
>> wrote:
>>> Hi,
>>> I have very specific problem. I have data and proto file available and 
>>> my application should take both and based on external configuration 
>>> determine how to interpret data (many different types/messages in proto). 
>>> Yet that can be determine only during run. My question is if there is any 
>>> support for that, I mean that I will be able to parse proto and decode data 
>>> based on content of interpret intermediate structures.
>>> I have been trying to analyze this possibility directly from codes but 
>>> not with much success. I would be glad for any guidance.
>>> -- 
>>> You received this message because you are subscribed to the Google 
>>> Groups "Protocol Buffers" group.
>>> To unsubscribe from this group and stop receiving emails from it, send 
>>> an email to protobuf+u...@googlegroups.com.
>>> To post to this group, send email to prot...@googlegroups.com.
>>> Visit this group at http://groups.google.com/group/protobuf.
>>> For more options, visit https://groups.google.com/d/optout.

You received this message because you are subscribed to the Google Groups 
"Protocol Buffers" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to protobuf+unsubscr...@googlegroups.com.
To post to this group, send email to protobuf@googlegroups.com.
Visit this group at https://groups.google.com/group/protobuf.
For more options, visit https://groups.google.com/d/optout.

Reply via email to