How to fix Python YAML namedtuple error: yaml.representer.RepresenterError: (‘cannot represent an object’, …


You are trying to yaml.safe_dump() an object which is (or contains) a namedtuple instance such as:

import yaml
import collections

MyTuple = collections.namedtuple("MyTuple", ["a", "b", "c"])
mytuple = MyTuple(1,2,3)


which results in the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/", line 269, in safe_dump
    return dump_all([data], stream, Dumper=SafeDumper, **kwds)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/", line 241, in dump_all
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/", line 27, in represent
    node = self.represent_data(data)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/", line 58, in represent_data
    node = self.yaml_representers[None](self, data)
  File "/home/uli/.local/lib/python3.10/site-packages/yaml/", line 231, in represent_undefined
    raise RepresenterError("cannot represent an object", data)
yaml.representer.RepresenterError: ('cannot represent an object', MyTuple(a=1, b=2, c=3))


You need to add a custom representer to implicitly convert your namedtuple to a dict.

Before running yaml.safe_dump(), add the following lines:

import collections

def represent_namedtuple(dumper, data):
    return dumper.represent_dict(data._asdict())

yaml.SafeDumper.add_representer(MyTuple, represent_namedtuple)

You need to add_representer() for every namedtuple you use!

Now, the yaml.safe_dump() call should work perfectly:

yaml.safe_dump(mytuple) # Returns 'a: 1\nb: 2\nc: 3\n'