support for Abstract Base Classes

[alex.garel@…]

problem

>>> import yaml
>>> from collections import Mapping
>>> class A(Mapping):
...     pass
... 
>>> yaml.dump(A)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/tmp/yaml/lib/python2.7/site-packages/yaml/__init__.py", line 202, in dump
    return dump_all([data], stream, Dumper=Dumper, **kwds)
  File "/tmp/yaml/lib/python2.7/site-packages/yaml/__init__.py", line 190, in dump_all
    dumper.represent(data)
  File "/tmp/yaml/lib/python2.7/site-packages/yaml/representer.py", line 28, in represent
    node = self.represent_data(data)
  File "/tmp/yaml/lib/python2.7/site-packages/yaml/representer.py", line 61, in represent_data
    node = self.yaml_multi_representers[data_type](self, data)
  File "/tmp/yaml/lib/python2.7/site-packages/yaml/representer.py", line 408, in represent_object
    reduce = data.__reduce_ex__(2)
  File "/tmp/yaml/lib/python2.7/copy_reg.py", line 70, in _reduce_ex
    raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle int objects

analysis

This is because of A being handled as an object, so an unbind version object.__reduce_ex__ is called, so protocol version is mistaken with the object (2 is passed in place of self).

>>> type(A)
<class 'abc.ABCMeta'>

solution

>>> from yaml.representer import Representer
>>> from abc import ABCMeta
>>> Representer.add_representer(ABCMeta, Representer.represent_name)
>>> yaml.dump(A)
"!!python/name:__main__.A ''\n"