I have a protobuf string representation for some object (__str___() def). Is it possible easily create that object from that string? Or the only possible way is the self written parser?
Default serialization\deserialization is not applicable since the object state modification should be performed outside of the programming scope. And the whole flow is following:

get ser representation from network;
deser this representation to the object;
get the string representation for the object;
pass this representation to somebody who wants change some fields
(values changed in the string representation). here will be created
a separate file with the str representation for all received objects
(there will be lots of objects);
convert NEW string to the Py object;
Ser object;
Pass ser message over network.
It will depend on how you represent the object as str(). If the object is machine parseable, you will have the best luck. If you use json, yaml or xml, you can use built in serialization libraries, otherwise you'll need to roll your own.
Is it possible to create an object from the protobuf str representation in Python