Nested classes can't be deserialized

[MoritzMaxeiner]

Trying to serialize and then deserialize a nested class like

import yaml

class A:
    class B:
        def __init__(self, i):
            self.i = i
    def __init__(self, i):
        self.b = A.B(i)

yaml.load(yaml.dump(A(0)))

with pyyaml 3.12 (python 3.6) yields an exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/__init__.py", line 72, in load
    return loader.get_single_data()
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 37, in get_single_data
    return self.construct_document(node)
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 46, in construct_document
    for dummy in generator:
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 578, in construct_python_object
    state = self.construct_mapping(node, deep=deep)
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 204, in construct_mapping
    return super().construct_mapping(node, deep=deep)
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 129, in construct_mapping
    value = self.construct_object(value_node, deep=deep)
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 91, in construct_object
    data = next(generator)
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 575, in construct_python_object
    instance = self.make_python_instance(suffix, node, newobj=True)
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 552, in make_python_instance
    cls = self.find_python_name(suffix, node.start_mark)
  File "/home/calrama/.local/lib64/python3.6/site-packages/yaml/constructor.py", line 529, in find_python_name
    % (object_name, module.__name__), mark)
yaml.constructor.ConstructorError: while constructing a Python object
cannot find 'B' in the module '__main__'
  in "<unicode string>", line 2, column 4:
    b: !!python/object:__main__.B {i: 0}
       ^

Without nesting B in A it works as expected:

import yaml

class B:
    def __init__(self, i):
       self.i = i

class A:
    def __init__(self, i):
        self.b = B(i)

yaml.load(yaml.dump(A(0)))

The obvious workaround of just not using nesting is not always easily applicable when e.g. working with classes exposed from C/C++ (especially with C/C++ enumerations exposed as nested classes).

[egafni]

bump, this is still a problem