grc: embedded python objects fail to load because of missing cpp_templates

[mormj]

AttributeError: 'EPyBlock' object has no attribute 'cpp_templates'
This is with latest master edaa88f

Reproduce by opening a blank flowgraph in grc, and adding "Python Block" or "Python Module"

Going to see if there is an easy fix, but wanted to go ahead and post the issue

[mormj]

As the classes that derive from block load and get passed to this decorator, the flags accumulate in all the classes

dummy - {}
epy_block - {show_id}
virtual_source - {show_id, cpp}
...

so by the time virtual source is added, the full list build_ins in each class has all the flags

def register_build_in(cls):
    cls.loaded_from = '(build-in)'
    build_ins[cls.key] = cls
    return cls

[dkozel]

Do you know what changed caused these blocks to stop working?

[mormj]

Looks like some of the recent cpp_template changes. The underlying issue that these blocks have flags that they shouldn't was probably always there, but the recent change to access the cpp_templates member of a block is new, and that's where the exception was occuring