theme theme-name doesn't have "theme" setting for customizing my theme in sphinx?

I want to create my own theme--mytheme for python-sphinx.

tree project
project
├── build
├── make.bat
├── Makefile
├── mytheme
│   ├── static
│   │   └── style.css
│   └── theme.conf
└── source
    └── conf.py

Content in theme.conf:

cat  project/mytheme/theme.conf
[theme]
inherit = default
stylesheet = style.css

Conent in project/source/conf.py

cat project/source/conf.py
def setup(app):
    app.add_stylesheet('static/style.css')
    app.add_html_theme('mytheme', os.path.abspath(os.path.dirname(__file__)))

html_theme = 'mytheme'  
html_theme_path = ['.']

Now let's make all my *.rst file in source.

cd project
make html
Running Sphinx v2.4.4
loading pickled environment... done

Theme error:
theme 'mytheme' doesn't have "theme" setting
Makefile:19: recipe for target 'html' failed
make: *** [html] Error 2

How to fix it ?

Solution

You use two mutually exclusive approaches - using local theme from filesystem, and at the same time register theme as it is done in themes distributed as Python PyPI package.

If you want a theme to be a part of the Sphinx project, good place for such project-specific themes is _themes/ in the directory with conf.py, and set html_theme = "mytheme" and html_theme_path = ["_themes"] in your conf.py.

_themes/
    mytheme/
        static/
            css/
                main.css
        theme.conf
        layout.html
conf.py
index.rst
second.rst
third.rst
...

(borrowed from https://blog.documatt.com/sphinx-theming/themes.html#project-specific-themes)

Completely delete block

def setup(app):
    app.add_stylesheet('static/style.css')
    app.add_html_theme('mytheme', os.path.abspath(os.path.dirname(__file__)))

add_html_theme() it is for themes distributed as a package. add_stylesheet() is to add additional (not replace existing) stylesheet. Themes main stylesheet is in their theme.conf stylesheet option.

The last issue I see in your example is your theme inherit from default theme. It works, it looks it's an old name for classic theme (https://www.sphinx-doc.org/en/master/usage/theming.html#builtin-themes), but use its official name - classic.