Toml Version 0.10.1 regression as compared to 0.10.0: ValueError: Circular reference detected

[JoeJasinski]

Hi all,
This dictionary below cannot be serialized to toml in 0.10.1, but it was able to be serialized in 0.10.0. (This is a simplified output that was generated by the https://github.com/jupyterhub/traefik-proxy project). According to the commit history, some changes went in place to raise the Circular reference detected. However, I'm not sure how the below dict would be considered a circular reference, and considering it worked with 0.10.0, it seems odd that it would be considered one now. I'm able to serialize with yaml without issue, for example.

{'backends': {'backend__2Fdsadmin_2Fhub_2F': {},
                  'backend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F': {},
                  'backend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F': {},
  },
 'frontends': {'frontend__2Fdsadmin_2Fhub_2F': {'routes': {'test': {}}},
               'frontend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F': {'routes': {'test': {}}},
               'frontend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F': {'routes': {'test': {}}},
}}

Steps to reproduce with toml==0.10.1

$ docker run -it python:3.8.2 bash
root@f89cdc41e3af:/# pip install toml==0.10.1
Collecting toml==0.10.1
  Downloading toml-0.10.1-py2.py3-none-any.whl (19 kB)
Installing collected packages: toml
Successfully installed toml-0.10.1
WARNING: You are using pip version 20.0.2; however, version 20.1.1 is available.
You should consider upgrading via the '/usr/local/bin/python -m pip install --upgrade pip' command.
root@f89cdc41e3af:/# pip install pyyaml==5.3.1 # for comparrision
Collecting pyyaml==5.3.1
  Downloading PyYAML-5.3.1.tar.gz (269 kB)
     |████████████████████████████████| 269 kB 3.1 MB/s 
Building wheels for collected packages: pyyaml
  Building wheel for pyyaml (setup.py) ... done
  Created wheel for pyyaml: filename=PyYAML-5.3.1-cp38-cp38-linux_x86_64.whl size=572452 sha256=38dad2849fb02e58540047a6018b3125733f050fafbe323d39546b7fb4bd3fb5
  Stored in directory: /root/.cache/pip/wheels/13/90/db/290ab3a34f2ef0b5a0f89235dc2d40fea83e77de84ed2dc05c
Successfully built pyyaml
Installing collected packages: pyyaml
Successfully installed pyyaml-5.3.1
WARNING: You are using pip version 20.0.2; however, version 20.1.1 is available.
You should consider upgrading via the '/usr/local/bin/python -m pip install --upgrade pip' command.
root@f89cdc41e3af:/# 
root@f89cdc41e3af:/# python
Python 3.8.2 (default, Feb 26 2020, 14:58:38) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 
>>> import yaml
>>> import toml
>>> d = {'backends': {'backend__2Fdsadmin_2Fhub_2F': {},
...                   'backend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F': {},
...                   'backend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F': {},
...   },
...  'frontends': {'frontend__2Fdsadmin_2Fhub_2F': {'routes': {'test': {}}},
...                'frontend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F': {'routes': {'test': {}}},
...                'frontend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F': {'routes': {'test': {}}},
... }}
>>> 
>>> print(yaml.dump(d))
backends:
  backend__2Fdsadmin_2Fhub_2F: {}
  backend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F: {}
  backend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F: {}
frontends:
  frontend__2Fdsadmin_2Fhub_2F:
    routes:
      test: {}
  frontend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F:
    routes:
      test: {}
  frontend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F:
    routes:
      test: {}

>>> toml.dumps(d)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.8/site-packages/toml/encoder.py", line 67, in dumps
    raise ValueError("Circular reference detected")
ValueError: Circular reference detected

Steps to show successful serialization with toml==0.10.0

$ docker run -it python:3.8.2 bash
root@9f40631841db:/# pip install toml==0.10.0
Collecting toml==0.10.0
  Downloading toml-0.10.0-py2.py3-none-any.whl (25 kB)
Installing collected packages: toml
Successfully installed toml-0.10.0
WARNING: You are using pip version 20.0.2; however, version 20.1.1 is available.
You should consider upgrading via the '/usr/local/bin/python -m pip install --upgrade pip' command.
root@9f40631841db:/# 
root@9f40631841db:/# python
Python 3.8.2 (default, Feb 26 2020, 14:58:38) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 
>>> import toml
>>> d = {'backends': {'backend__2Fdsadmin_2Fhub_2F': {},
...                   'backend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F': {},
...                   'backend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F': {},
...   },
...  'frontends': {'frontend__2Fdsadmin_2Fhub_2F': {'routes': {'test': {}}},
...                'frontend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F': {'routes': {'test': {}}},
...                'frontend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F': {'routes': {'test': {}}},
... }}
>>> 
>>> toml.dumps(d)
'[backends.backend__2Fdsadmin_2Fhub_2F]\n\n[backends.backend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F]\n\n[backends.backend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F]\n\n[frontends.frontend__2Fdsadmin_2Fhub_2F.routes.test]\n\n[frontends.frontend__2Fdsadmin_2Fhub_2Fuser_2Fjoe_2Ej_40example_2Ecom_2F.routes.test]\n\n[frontends.frontend__2Fdsadmin_2Fhub_2Fuser_2Fkrombo_2Emichael_40example_2Ecom_2F.routes.test]\n'
>>> 

[Edward-Knight]

Seems to be a duplicate of #295 - I believe it's caused by the empty dictionary

[Edward-Knight]

Can confirm is fixed by 9be6458, just tried your example myself on master

[uiri]

Duplicate of #295