in `_check_toc_entries`, `sections` is assumed to be a dict but a string was passed

Describe the bug

Unfortunately this is in the middle of a repo I’m changing a lot and I can’t push the changes that cause this up yet, sorry about that. Below is the info I best have and I hope it’s sufficient to understand the issue, if not I’ll try to clean up my example so it’s reproducible, but perhaps this is enough to point in the right direction…

Using j-book 0.9.1 on a Mac (python 3.8), with the following _toc.yml file:

# Table of contents
# Learn more at https://jupyterbook.org/customize/toc.html

# First entry here is the website/book's landing page.
- file: overview

# The rest is structured in *parts* that then have chapters/sections.

- part: Overview
  chapters:
  - file: schedule
  
- part: Syllabus
  chapters:
    file: syllabus

- part: Homework Assignments
  numbered: true
  chapters:
    file: Hw/hw01-background.md

- part: Lecture Notes
  chapters:
  - file: Notes/01/index

when running jupyter-book build . I get this error:

Extension error:
Handler <function add_toc_to_sphinx at 0x7fa5bf83d5f0> for event 'config-inited' threw an exception (exception: 'str' object has no attribute 'keys')
Traceback (most recent call last):
  File "/Users/fperez/local/conda/lib/python3.7/site-packages/sphinx/events.py", line 110, in emit
    results.append(listener.handler(self.app, *args))
  File "/Users/fperez/.local/lib/python3.7/site-packages/jupyter_book/toc.py", line 175, in add_toc_to_sphinx
    _check_toc_entries([toc])
  File "/Users/fperez/.local/lib/python3.7/site-packages/jupyter_book/toc.py", line 376, in _check_toc_entries
    _check_toc_entries(section[section_kind])
  File "/Users/fperez/.local/lib/python3.7/site-packages/jupyter_book/toc.py", line 376, in _check_toc_entries
    _check_toc_entries(section[section_kind])
  File "/Users/fperez/.local/lib/python3.7/site-packages/jupyter_book/toc.py", line 356, in _check_toc_entries
    for key in section.keys():
AttributeError: 'str' object has no attribute 'keys'

This is the file layout of that repo, in case it helps:

drwxr-xr-x  4 fperez    128 Jan 18 11:24 Hw/
drwxr-xr-x  3 fperez     96 Jan 16 14:26 Notes/
-rw-r--r--  1 fperez    212 Jan 15 10:47 README.md
drwxr-xr-x  5 fperez    160 Jan 17 15:57 _build/
-rw-r--r--  1 fperez    770 Jan 18 07:50 _config.yml
-rw-r--r--  1 fperez    475 Jan 18 11:25 _toc.yml
-rw-r--r--  1 fperez   9854 Jan 17 15:50 logo.png
-rw-r--r--  1 fperez   7368 Jan 18 11:08 overview.md
-rw-r--r--  1 fperez  12058 Jan 17 15:33 schedule.md
-rw-r--r--  1 fperez  10983 Jan 16 16:15 syllabus.md

Again, sorry for the partial report!! LMK if it’s not enough and I’ll work on a cleaner one 😃

[fperez]

Yup! The list/dict confusion was actually a yaml mistake of mine, due to being quite the yaml newbie… I didn’t actually realize this defined different yaml data structures, and so I was pretty confused by the error msg.

So my bad on that front, but the jbook validation could probably assist anyone who is similarly not very adept at spotting these yaml nuances.

Thanks a lot for the quick response!

[choldgraf]

I’m gonna close this one since I think we’ve got it figured out, and I have opened up https://github.com/executablebooks/jupyter-book/issues/1200 to track improving the error messages that are associated with these YAML config missteps.