CHM is getting too hard to handle (see e.g. bpo-47051 for the latest issue), so let's just bite the bullet and ship the HTML docs instead.

New changeset 3751b6b by Steve Dower in branch 'main':
bpo-47086: Remove .chm from Windows installer and add HTML docs (GH-32038)
3751b6b

Leaving this open and assigned to myself for a couple of days to deal with any other fallout. In particular, I wasn't able to test the (minor) changes to the publishing steps (e.g. GPG signing), so will have to wait for the next release to see what works/doesn't there.

If you remove the .chm file from the Windows installer, I believe IDLE needs to be updated to look for the installed html files instead (see Lib/idlelib/editor.py).

And does this mean we should no longer produce .chm files at all for 3.11+? If so, there is work to be done in the Doc section of the repo (Makefile, make.bat, README.rst tools/* all have references to .chm and .hhp files). I guess other than the references to chm files in the docs, this change would not otherwise affect the on-line docs building system.

(Nosying Terry and Julien as subject experts.)

Good call on IDLE, I didn't even think to check there (there is a registry key that points at the documentation if it was installed, which would be the best approach for IDLE to use).

The makefiles don't urgently need to remove those references. If people still want to build it, they're welcome to [try]. It gives people with their own build processes a chance to adapt - we can remove it all later.

For the registry key, reading the default value from key "HKCU\Software\Python\PythonCore\{sys.winver}\Help\Main Python Documentation" (or HKLM - no need to worry about the Wow6432Node bit here) and passing it to os.startfile() will work for all active releases.

If the key is missing, so are the local docs, so falling back to the web docs is a fine option.

The key is defined at https://github.com/python/cpython/blob/main/Tools/msi/doc/doc.wxs#L17 and is not set for a Store install at all. But we don't include the docs in that either - go straight to the web.

Do you have any thoughts about distributing the docs in ePub format?

At a minimum, though, Doc/tools/templates/download.html should be changed to remove the chm reference.

Do you have any thoughts about distributing the docs in ePub format?

If Windows includes a reader for all supported versions, and it's easy
to build, sure. But I don't think the first bit is true.

Most people are going to be fairly comfortable with their default
browser, and many are going to greatly prefer it. I think loose HTML
files is a good option from every POV other than being a large number of
loose files.

Do you have any thoughts about distributing the docs in ePub format?

Note that it's *much* easier to manufacture the docs in html format than it is in ePub format.

In the IDLE Help menu, 'Python Docs', default hotkey 'F1', invokes '<<python-docs>>', which is handled by EditorWindow.help_docs. For Windows, line 599, is 'os.startfile(self.help_url)'. (Otherwise, webbrowser is used.) On Windows, help_url is os.path.join(sys.base_prefix, 'Doc','Python%s.chm' % _sphinx_version())
if the result is valid, else python.org/...(but '3.1' because only 3 chars are grabbed).

How do I use winreg to get the file name from
"HKCU\Software\Python\PythonCore\{sys.winver}\Help\Main Python Documentation"?
The winreg doc assumes some knowledge of registry terminology that I do not have and has no examples, so my attempts failed.

This should work for you (luckily, this is about the simplest possible case):

import sys
import winreg

def get_help():
    KEY = rf"Software\Python\PythonCore\{sys.winver}\Help\Main Python Documentation"
    try:
        return winreg.QueryValue(winreg.HKEY_CURRENT_USER, KEY)
    except FileNotFoundError:
        pass
    try:
        return winreg.QueryValue(winreg.HKEY_LOCAL_MACHINE, KEY)
    except FileNotFoundError:
        pass
    return f"https://docs.python.org/{sys.version_info.major}.{sys.version_info.minor}/"

New changeset fe01060 by Steve Dower in branch 'main':
bpo-47086: Remove dead link to old CHM documentation (GH-32075)
fe01060

CHM is totally removed? It is very good at search and fast navigating, rather than render all the documentation tree.
It would be good if user can compile it for itself, because this format is very handy over browser.

People can still compile the CHM themselves - use Doc\make.bat htmlhelp - though we aren't accepting fixes specifically for it anymore (e.g. to fix crashes due to unsupported characters in the index).