IDLE warns against an old TCL version even though I’ve installed a newer version

According to the “How Python Chooses Which Tk Library To Use” section of the “IDLE and tinter with Tcl/Tk on Mac OS X” page on the official python website,

The Python for Mac OS X installers downloaded from this website dynamically link at runtime to Tcl/Tk Mac OS X frameworks. The Tcl/Tk major version is determined when the installer is created and cannot be overridden. The Python 64-bit/32-bit Mac OS X installers for Python 3.4.x, 3.3.x, 3.2.x, and 2.7.x dynamically link to Tcl/Tk 8.5 frameworks.

So it seems that

1. The current python installations for OS X do not recognize the latest ActiveTcl version (namely 8.6).
2. The Tcl/Tk version used by python is hard-wired during the python installation procedure and cannot be changed later.

From these observation the solution is clear:

1. Install the latest 8.5 ActiveTcl version.
2. Reinstall python.

I have followed these steps and now everything seems to work.