Host the Python docs on ReadTheDocs

From time to time the discussion arise about moving docs.python.org to readthedocs, there's even an experimental python.readthedocs.io.

I think there's many pros and cons of using readthedocs.

I'd personally be in favor of it if we (the PSF) support them (the cpython Doc is a big one with a lot of traffic, it take around 24h of CPU to build all versions × languages with all PDF A4, PDF letter, HTML, plaintext, epub).

In the other hand it's not an easy task, among other things docs.python.org is not only about generating the docs but also hosting history:

https://docs.python.org/release/ (this is all the tagged commits in the cpython repo)
https://docs.python.org/2.0/ (yes we keep old versions, and I'm not willing to see this disapear)

@pradyunsg

ping @pradyunsg because you're speaking a lot about readthedocs :)
ping @humitos because you're from readthedocs :)

@hugovk

Disclaimer: I work at Read the Docs.

I think there's many pros and cons of using readthedocs.

I'm not going to start selling Read the Docs because that's not my topic 😄 --Currently, I'm more interested in making sure that "the migration is possible from the technical aspect" and mention some notes to consider.

I'd personally be in favor of it if we (the PSF) support them

What kind of support do you refer to here? Take into account that Read the Docs by default adds EthicalAds on the documentation it hosts. I suppose there may be some different opinions about this and I think it worth having a conversation about the different possibilities we can explore.

the cpython Doc is a big one with a lot of traffic, it take around 24h of CPU to build all versions × languages with all PDF A4, PDF letter, HTML, plaintext, epub

We are currently using Read the Docs for the Spanish translation of the CPython documentation. It takes ~500 seconds to build the HTML with our smallest builder (2 CPU, 2Gb RAM, -j auto). It takes ~500 seconds more to build the PDF

Each commit merged into an active branch from English, should trigger a re-build for all the translations to update them as well. So, one single merge will trigger 1 (version) x (8 languages) = 8 builds * ~1000 seconds = ~2 hours (is my math correct? 🤔 )

Edit: I put 8 versions originally, but that's not correct. Only one version is required to be built. The version where the merge was done. If it was done in 3.10, only 3.10 + its translations need to be re-built.

Edit: the unit of the result was incorrect. I changed "2 minutes" by "2 hours" thanks to @hugovk for noting this.

Take into account that translations may require some extra work to be able to clone CPython repository to get the source files. In the Spanish translation we are using a git submode for this and then changing the Sphinx.srcdir to point to it in the conf.py file.

Note that Read the Docs only support one PDF output file. So, all the pages are together in one big PDF file, instead of split into the tutorial and others as the current behavior. There is an issue to discuss supporting multiple PDF output at readthedocs/readthedocs.org#2045

among other things docs.python.org is not only about generating the docs but also hosting history:
https://docs.python.org/release/ (this is all the tagged commits in the cpython repo)

This page looks like a simple index of a directory containing all the versions. There is not a direct match of this to a feature on RTD that allows this listing. I'd suppose that you may need to create an RST file or include an HTML page that lists all the current releases.

Also, a URL like /release/ is not supported either. It needs to have a prefix of /lang/version/ on a multi-version project. However, a redirect could be created: /release/ -> /en/stable/release/.

https://docs.python.org/2.0/ (yes we keep old versions, and I'm not willing to see this disappear)

This shouldn't be a problem if there is a way to re-generate them (e.g. running sphinx-build from branch 2.0 works). Unfortunately, Read the Does does not support uploading pre-built documentation. See readthedocs/readthedocs.org#1083

To summarize, I think there some initial things bumped here:

Ads on documentation
building time (resource usage)
multiple PDF output
plaintext format not supported
build old releases
page listing all versions
translations may need extra work

Hopefully, this helps to understand some of the technical requirements and provides some value regarding the work effort required conversation.

Each commit merged into an active branch from English, should trigger a re-build for all the translations to update them as well. So, one single merge will trigger 1 (version) x (8 languages) = 8 builds * ~1000 seconds = ~2 minutes (is my math correct? 🤔 )

~8,000 seconds = ~133 minutes = ~2h13m

Edit: I put 8 versions originally, but that's not correct. Only one version is required to be built. The version where the merge was done. If it was done in 3.10, only 3.10 + its translations need to be re-built.

~1,000 seconds = ~17 minutes

Also, a URL like /release/ is not supported either. It needs to have a prefix of /lang/version/ on a multi-version project. However, a redirect could be created: /release/ -> /en/stable/release/.

We can mostly support custom URL's like this now. It's a beta feature, but if it's a blocker we can certainly manage it. That said, we don't currently support directory indexing, but we could create a version of the page thats branded properly in the docs theme.

What kind of support do you refer to here? Take into account that Read the Docs by default adds EthicalAds on the documentation it hosts. I suppose there may be some different opinions about this and I think it worth having a conversation about the different possibilities we can explore.

Just to be explicit, we're happy to host the Python docs without ads. I know there has been some discussion about having PSF sponsors included on the pages, and we've had separate conversations with the PSF team about us enabling that with our open source EthicalAds platform. We can definitely discuss having an additional business relationship with the PSF for hosting the docs, but I don't consider it a prerequisite. We get a lot of value out of Python, and are happy to support the projects we use heavily ad-free if needed (we already do this with Sphinx).

Unfortunately, Read the Does does not support uploading pre-built documentation. See readthedocs/readthedocs.org#1083

We could upload pre-built docs if they don't ever change as a one-off. It's not supported on the platform, but we can manually do it if needed.

I'm not going to start selling Read the Docs because that's not my topic 😄 --Currently, I'm more interested in making sure that "the migration is possible from the technical aspect" and mention some notes to consider.

Agreed. In the past there were some technical issues that would have prevented this, but I think we've solved most of them. We can do a bit more work to fully replicate the docs.python.org setup with existing URL's on our side if you'd like to see a tech demo, but we'd hope to do that after there was an agreement on moving to RTD from the team.

My primary non-technical selling point to hosting docs on RTD is that any work that goes into building features will now be shared with the entire Python community via RTD, instead of work done on a custom docs hosting tool. Similarly, any work the community does to improve RTD will automatically flow back to Python itself. Hopefully these additional resources will make doc hosting better for the whole ecosystem.

Please let us know if you have any questions about the product features or feasibility of hosting, as this progresses.

@pradyunsg

ping @pradyunsg because you're speaking a lot about readthedocs :)

Only because a lot of what the docs build scripts are doing, is something provided by RTD as well. 😅

And RTD has the benefit of being a platform, and thus being able to provide things like PR previews.

Just wanted to note that this might also be worth thinking about while we're doing #1. It would be awesome if we could get a new theme and not have to implement all the various Python-specific code to support it. We'd be interested in helping with this, if it was of interest.

Not sure what kind of 👍 we'd need to move forward on it, but I'd love to get more effort going into RTD integration instead of 1-off integrations of custom build logic. We've made good progress on a few of the above issues, and would be happy to do custom stuff for Python in the places where we don't have platform support.

I think it's a great idea to host the docs on Read the Docs:

transparency of builds for all, no need to bug someone to SSH in to a server
PR previews (we're using an RTD site just for this, it's extremely useful)
can have builds for each merge to the branch, no need to wait 24h+ for the cron
the RTD team are very responsive and helpful
RTD is open source and Python

We've been discussing this in docs-community monthly meetings and Discord, and there's seems to be support on moving forward.

We have a large build matrix of languages. versions, and output formats (HTML, PDF, EPUB, etc). I would suggest an incremental approach, starting with just English, dev and and HTML.

Once we're happy with it, we can remove that particular build from the server and add another language/version/output.

Perhaps doing English+HTML first for the main builds (currently /dev, /3 and maybe /3.11) will give the biggest initial benefit. Then other languages+HTML. It might be that we keep some builds on the server for much longer, like PDF/EPUB etc. I think this is fine, the reduced load of moving HTML builds off the server will improve the queue time for other builds.

More concretely, I think the first thing to do is deal with the HTML language/version switcher. Currently this is added on the server builds via https://github.com/python/docsbuild-scripts.

We'll need a similar switcher for RTD builds.

I don't think it necessarily needs to be identical to the legacy one, but should be similar because people will be switching to/from the old and new sites.

We would develop it on something like https://cpython-previews.readthedocs.io (which is used for PR previews) and when happy, switch https://docs.python.org to it, stop the old server HTML build, and move to the next increment.

Thoughts?

@ewdurbin

Thoughts?

I don't know how RTD survives financially today (yes I know it has been very hard).

Building more often that we build now (for every push, with PDF US letter, PDF A3, epub, txt, downloadable HTML) will take a lot of resources, more than the 4 virtual CPU that we already use 24h/24h.

I also don't know how RTD pays for the bandwidth, but I bet docs.python.org consumes some bandwidth (@ewdurbin any numbers?), it's probably nothing compared to PyPI but yet, let's check that. PSF side the bandwidth is sponsored by Fastly, but RTD side I don't know...

I think that the PSF and RTD should talk about money here: the PSF have to ensure, at the very least, that we don't penalize RTD. But it's not enough, I think the PSF should back up RTD in case RTD looses a vital sponsor (CPU/bandwidth provider or something) to ensure the future. @ericholscher @ewdurbin.

My non-financial view on this: RTD has proven they are the Python documentation hosting platform. Using RTD will make cpython a good citizen of the ecosystem. In other words, There should be one-- and preferably only one --obvious way to do it., and it's clearly not our little snowflake.

Building more often:

If we don't want to build every merge, we can write a custom command to skip builds. For example, we should only do so for Doc/ changes, and could come up with extra logic to limit builds.

Docs: https://docs.readthedocs.io/en/stable/build-customization.html#cancel-build-based-on-a-condition

Some numbers:

During the 30-day Plausible trial, we had 6.5 million total visits and 10.9 million pageviews to the 3.11 and 3=3.12 English sites.

We could feasibly add a proxy/cache via Fastly to read the docs, we do this for PEPs. That might also solve keeping /2.0/ &c.

A

Echoing support for the proxy/cache concept, I don't think there was ever a philosophical objection to hosting on RTD, just technical and sustainability questions. Both the PSF and RTD are much better equipped these days to have the sustainability discussion directly between PSF and RTD staff than either were back when RTD was still relatively new, which leaves the technical side of things for the docs community to consider.

If the existing Fastly + Nginx docs endpoint is retained, with just the build and hosting of the version specific docs for actively maintained versions shifted to RTD, then it may be feasible to migrate new docs builds without needing to worry about too many one-off CPython-docs-specific hosting capabilities in RTD (instead leaving those in the existing PSF infrastructure).

I do think it would be important to be explicit about the intended benefits of the hosting change, though. As far as I am aware, the main CPython docs builds are still just periodic (daily?), which would make the commit triggered builds in RTD one of the biggest improvements on offer.

Another benefit of using Read the Docs is the server side search.

@humitos

Just wanted to chime in here from the RTD perspective. RTD has a similar relationship with sponsored CDN hosting, where we aren't paying for bandwidth. So we don't have much worry about traffic or CDN support there. If it's a benefit to y'all to be able to put your own CDN in front, that's something we can support, but we already have our CDN configured to purge automatically on build, redirects, and other settings change, which won't flow through. That's likely not a huge deal, but might lead to delays in content changes, so something to consider.

I don't want to block this discussion on sustainability -- RTD is able to host the Python docs without any specific payment -- as noted above we're in a much better place these days, with our server costs and CDN sponsored and a full-time team working on the platform. We would still love some kind of support from the PSF, but it's not required. We'd just ask that the fact that RTD is hosting it is shown somewhere on the pages, perhaps in the footer.

Overall, we're excited to be able to host the official Python docs, and want to work with y'all to make it successful. I know @humitos has already chimed in here, but we're both available to answer any questions that y'all might have, as needed.

Yes, or would it be better to have the URLs in a file hosted outside the CPython repo?

Cool. I will try to find some time this week to open a PR and we can discuss there the best approach so we don't deviate this issue this technical details.

Hmm, these names are already taken but abandoned:
readthedocs.org/projects/python - by some guy named Eric :)

Heh, yeah, this was created as a mirror and as a way to reserve the name as well. I'm sure we can free this slug and use it for Python itself 😄 . I will ask Eric just in case, tho.

readthedocs.org/projects/cpython - by a third party

Indeed, this project is abandoned and we can follow https://docs.readthedocs.io/en/stable/abandoned-projects.html to recover the slug.

In case both are available, which one do you prefer: cpython or python?

Do you think we should rename the existing cpython-previews (used for PR previews) to one of those, or set one of those up as a new account?

We can, yes. It will require re-building all the versions and languages after changing the slug; but I think that's not an issue.

But yes to a proxy, when we have the first one ready to go. So let's get a demo working with a single version/language still on RTD first, test that out, then proxy it.

Excellent 💯

Generate version selector dynamically via JavaScript

After working on python/docsbuild-scripts#179 and finding myself blocked there, I took a deeper look at the PR that moves the selectors into the theme (python/python-docs-theme#193) and generate them at build time.

Since we talked about start serving one version on Read the Docs first and configure a proxy on docs.python.org to serve that version directly from Read the Docs, there is no need to use Read the Docs Addons API (yet) to generate the selectors as we are currently doing in https://cpython-previews.readthedocs.io/en/main/ because we won't have all the available versions hosted on Read the Docs and the API won't return all of them.

Something like the PR that generate the selectors at build time using external files (.json for the versions and .toml for the languages) would be enough to build on Read the Docs at this time and also building using the current docsbuild-script as well with the correct selectors.

Here is my proposal to continue with the migration of the documentation to Read the Docs in gradual phases:

Migration proposal to host docs on Read the Docs

Phase I: initial version migrated

Setup cpython or python project on Read the Docs.
Merge the PR that generate the switchers at build time (Add language and version switchers python-docs-theme#193).
Build one version on Read the Docs and check that everything is fine (e.g. 3.10).
Configure the proxy on docs.python.org to serve that version from Read the Docs. This is https://docs.python.org/3.10/ should proxy to https://cpython.readthedocs.io/en/3.10/ for example.

With that, we should have everything in place for the initial tests.

Phase II: add another version

Once we are happy with the previous tests, we can add more versions/languages to Read the Docs:

Activate a new version on Read the Docs to build it (e.g. 3.11).
Configure the proxy to point the new version to be served from Read the Docs.

Phase III: add another language

If everything is going well with the versions added, we can follow with translations/languages:

Setup cpython-{language} project on Read the Docs.
Activate and build all the versions we want for this translation.
Configure the proxy to point the new language to be served from Read the Docs.

Phase IV: final

At some point we will have added all the versions and languages to Read the Docs and there won't be more builds happening outside Read the Docs.

Remove the code to generate the selectors at build time and use the Read the Docs Addons API directly (see https://github.com/python/cpython/blob/main/Doc/tools/static/rtd_switcher.js)
Setup docs.python.org as canonical domain on Read the Docs
Delete configuration for the proxy

Let me know if this proposal makes sense or you think we should adapt it. I tried to make one step at a time to be able to revert the changes if something goes in an unexpected way. I'm happy to receive feedback and work together with any modification you may have to the proposal.

Thanks, this sounds like a good plan. 👍

(Little nitpick, although I know the examples versions are just to illustrate :) 3.10 and 3.11 are in security-only phase, so we try not to touch them. 3.12 aka /3/ is the most visited, so best not to start with that, probably dev version 3.14 first, then pre-release 3.13.)

one consideration is the long tail legacy documentation hosted on docs.python.org. there’s quite a bit.

it seems certainly preferable to move to hosting to RTD for the whole domain due to cache invalidation alone.

is there any way for us to host the older versions on RTD or will we need to keep fronting with Fastly to split traffic between branches built on RTD and the rest?

many of the files on the backends are probably safe to consider static. if we moved them to an object store like AWS S3, is it possible to have RTD handle routing to them?

is there any way for us to host the older versions on RTD or will we need to keep fronting with Fastly to split traffic between branches built on RTD and the rest?

There are a few possibilities here that we can explore if needed.

I started creating a proof of concept with the idea I consider is the best approach. It consists on downloading the HTMLZip for the old "static" version we want to serve from Read the Docs, and manually upload it skipping the normal build process.

I followed these steps:

Download the HTML .tar.bz2¹ version 3.9 for the Spanish translation² from https://docs.python.org/es/3.9/download.html
Upload its content to Read the Docs' S3 bucket next to the other versions of the project
Manually create a new 3.9 version for the project in the database

The result can be seen at https://cpython-previews.readthedocs.io/es/3.9/

As it follows the standard Read the Docs pattern but only skipping the build process, everything keeps working as if the version would have been built on Read the Docs:

the flyout (and version selector) shows 3.9 as an available version
the 3.9 version is listed in the dashboard's list of versions: https://app.readthedocs.org/projects/cpython-previews-es/
it can be hidden from the dashboard in case you don't want to expose it to your users
it can be eventually de-activated from the dashboard to delete it permanently

The only differences are:

there is no build logs for this version
this version cannot be re-built³

Let me know if all of this makes sense to you and if you have any doubt.

I'm not sure if this file is exactly the same version that is hosted at https://docs.python.org/es/3.9/ --if it's not, you can provide the correct one to upload ↩
I chose this version as an example, but it could be anyone ↩
In case rebuilding is strictly needed at some point in the future we can either follow this same approach to re-upload it, or reconfigure this version to be built on Read the Docs ↩

probably dev version 3.14 first, then pre-release 3.13

Makes sense to me 👍🏼

I wanted to quickly write to apologise as I haven't had the time needed to give this a considered response yet -- I hope to do so on Monday.

A

@AA-Turner

@AA-Turner friendly ping 😊. I'd really like to know your thoughts about this migration plan

Setup cpython-{language} project on Read the Docs.

Nit-picky comment to the migration plan: could the name for language repos be python-{language}? I believe this documentation documents more than just one implementation (contains ABI docs as well), so using python instead of cpython for identification shouldn't be an abuse.

Hi everybody 👋🏼

I just want to let you know that Read the Docs now supports direct upload. That means that you can build your documentation somewhere else (eg. CI, GitHub Action, your laptop, etc) and run a command to upload them to Read the Docs so they are served from it; while keeping all the hosting features: versioning, translations, visual diff, automation rules, etc. Read more about it at the documentation page: https://docs.readthedocs.com/platform/latest/guides/build/direct-upload.html

It's worth to note that this is still in beta and it's enabled via support request. However, it has been working great in our testing and we are happy to share this with you all. I know that https://github.com/python/docsbuild-scripts exists for a reason and you are already using the PR preview builds on Read the Docs via https://app.readthedocs.org/projects/cpython-previews/, so I thought it could be interesting for your use case. Let me know any feedback you may have.

@humitos

@humitos cool, thanks for letting us know!

One thing I'm not sure about, however, is how this would work with our CDN (Fastly), does RtD have support for such things?

Read the Docs has its own CDN (Cloudflare), so we wouldn't need to put our own in front of it.

https://docs.readthedocs.com/platform/latest/reference/cdn.html

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Host the Python docs on ReadTheDocs #5

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Migration proposal to host docs on Read the Docs

Phase I: initial version migrated

Phase II: add another version

Phase III: add another language

Phase IV: final

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Host the Python docs on ReadTheDocs #5

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JulienPalard commented on May 11, 2021

humitos commented on May 11, 2021

hugovk commented on May 11, 2021

ericholscher commented on May 11, 2021

pradyunsg commented on May 11, 2021

ericholscher commented on Nov 29, 2021

hugovk commented on Jan 19, 2024

JulienPalard commented on Jan 19, 2024

hugovk commented on Jan 19, 2024

AA-Turner commented on Jan 20, 2024

ncoghlan commented on Jan 23, 2024

methane commented on Jan 23, 2024

ericholscher commented on Jan 23, 2024

19 remaining items

humitos commented on Jul 23, 2024

humitos commented on Jul 23, 2024

Migration proposal to host docs on Read the Docs

Phase I: initial version migrated

Phase II: add another version

Phase III: add another language

Phase IV: final

hugovk commented on Jul 24, 2024

ewdurbin commented on Jul 24, 2024

humitos commented on Jul 25, 2024

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humitos commented on Jul 25, 2024

AA-Turner commented on Jul 29, 2024

humitos commented on Aug 16, 2024

m-aciek commented on Sep 8, 2024

humitos commented on Sep 21, 2026

StanFromIreland commented on Sep 21, 2026

hugovk commented on Sep 21, 2026

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