Read the Docs autodoc seems to fail on Python 3.6 formatted string

Question

I'm using the Sphinx autodoc feature in making documentation for my Python project. Building the HTML locally works fine, but it seems to fail on Read The Docs. I have RTD connected to my Github account, with a hook on commit. It seems to be reading my code and importing the package just fine.

The error I see seems to indicate that it's failing because of the formatted strings in my Python code:

WARNING: autodoc: failed to import module 'letterboxd.api'; the following exception was raised:
Traceback (most recent call last):
  ...
  File "/home/docs/checkouts/readthedocs.org/user_builds/letterboxd/envs/latest/lib/python3.5/site-packages/letterboxd-0.1.0a5-py3.5.egg/letterboxd/api.py", line 77
    headers["Authorization"] = f"Bearer {self.user.token}"
                                                         ^
SyntaxError: invalid syntax

I am running Python 3.6 locally, so my guess is that the issue may be that Read the Docs doesn't support 3.6 yet. I do have the RTD Admin > Advanced Settings > Python interpreter set to CPython 3.x, and have also checked the box for “Install your project inside a virtualenv using setup.py install”

Is this currently a known issue with RTD, or is there some setting I can tweak to correct this?

Answer 1

Based on the bug link that @sehafoc provided in a comment above (thanks!), I read and clicked through to find this doc page about building a YAML config file for RTD.

Adding this config file resolved this issue, where build:image: and python:version: are the relevant bits:

# .readthedocs.yml

build:
  image: latest

python:
  version: 3.6
  setup_py_install: true

requirements_file: requirements.txt