incompatibility - empty optional attributes are None instead of not existing

[oranch]

When parsing a message, optional attributes which don't have a value are created with a None value.
This is incompatible with the Google implementation, which does not create the attribute at all.

BTW this tool is great - keep up the good work :-)

[oranch]

I'm far from an expert on writing Python types, but looking at the code, I realize that getting hasattr() and getattr() right might be tricky, especially for native types where you can't use NULL in c++.

An easier improvement to compatibility would be to add new fields to the python class, named has - one for each optional attribute.

Such fields exist in the Google python implementation, so users would be able to safely alternate between the two implementations if they rely on these fields to test the existence of a value rather than on hasattr()

[oranch]

the comment system slightly messed up my last comment :-(
the field name is _has_xxxx for an attribute name of xxxx.