On 08/04/2016 09:11 AM, Alexander Belopolsky wrote:

Furthermore, the 3.4 release notes contain a warning
saying "The Argument Clinic PEP is not fully up to date with the state
of the implementation."  It does not look like this situation has
improved since.

It hasn't. The PEP lags behind the implementation. The HOWTO is up-to-date though.

The practical question is: does it make sense to invest time in
learning the clinic DSL and converting more modules (e.g. datetime) to
it or it is likely that the whole approach will be revised in the
future?

AFAIK the Clinic DSL can handle all of Python's C extensions. I have no plans to "revise the whole approach"; if someone else does I haven't heard about it.

/arry