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如何修复 Python yaml.representer.RepresenterError: ('cannot represent an object', defaultdict(<class 'list'>, ....

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问题：

你正在尝试 yaml.safe_dump() 一个是（或包含）defaultdict 的对象，例如：

yaml_fix.py
import yaml
import collections

yaml.safe_dump(collections.defaultdict(list))

这会导致以下异常：

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'>, {}))

解决方案

你需要添加自定义表示器来隐式将 defaultdict 转换为 dict。

在运行 yaml.safe_dump() 之前，添加以下行：

represent_defaultdict_fix.py
import collections
from yaml.representer import Representer

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

现在，yaml.safe_dump() 调用应该完美工作：

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