Как исправить Python yaml.representer.RepresenterError: ('cannot represent an object', defaultdict(<class 'list'>, ....

Проблема:

Вы пытаетесь выполнить yaml.safe_dump() для объекта, который является (или содержит) defaultdict, например:

yaml_fix.py

import yaml
import collections

yaml.safe_dump(collections.defaultdict(list))

import yaml
import collections

yaml.safe_dump(collections.defaultdict(list))

что приводит к следующему исключению:

yaml_repr_error.py

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/__init__.py", line 269, in safe_dump
    return dump_all([data], stream, Dumper=SafeDumper, **kwds)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/__init__.py", line 241, in dump_all
    dumper.represent(data)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/representer.py", line 27, in represent
    node = self.represent_data(data)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/representer.py", line 58, in represent_data
    node = self.yaml_representers[None](self, data)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/representer.py", line 231, in represent_undefined
    raise RepresenterError("cannot represent an object", data)
yaml.representer.RepresenterError: ('cannot represent an object', defaultdict(<class 'list'>, {}))

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/__init__.py", line 269, in safe_dump
    return dump_all([data], stream, Dumper=SafeDumper, **kwds)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/__init__.py", line 241, in dump_all
    dumper.represent(data)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/representer.py", line 27, in represent
    node = self.represent_data(data)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/representer.py", line 58, in represent_data
    node = self.yaml_representers[None](self, data)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/representer.py", line 231, in represent_undefined
    raise RepresenterError("cannot represent an object", data)
yaml.representer.RepresenterError: ('cannot represent an object', defaultdict(<class 'list'>, {}))

Решение

Вам нужно добавить пользовательский репрезентатор для неявного преобразования defaultdict в dict.

Перед запуском yaml.safe_dump() добавьте следующие строки:

represent_defaultdict_fix.py

import collections
from yaml.representer import Representer

yaml.SafeDumper.add_representer(collections.defaultdict, Representer.represent_dict)

import collections
from yaml.representer import Representer

yaml.SafeDumper.add_representer(collections.defaultdict, Representer.represent_dict)

Теперь вызов yaml.safe_dump() должен работать идеально:

yaml_safe_dump_defaultdict_fixed.py

yaml.safe_dump(collections.defaultdict(list)) # Returns'{}\n'

yaml.safe_dump(collections.defaultdict(list)) # Returns'{}\n'