Is there a known date/timeframe when python 2.7 will not be supported any more in favor of python 3?
In May 2010, Word of God was that patchlevel releases for Python 2.7 will probably be made for at least 6 years.
So, maybe 2016, probably later.
Edit: Pushed back to 2020. See the revision to PEP 373, linked to in other answers.
This article says: “When 2.7 is released, the 2.x line will move into five years of a bug fix-only mode.”
So, as far as I see, Python 2.7 was the last 2.x feature-adding release, and though found bugs are going to be fixed (for some time), new features only go to 3.x releases.
The Python Developer’s Guide lists the "Status of Python branches" from version 2.6 up to the current version, including their current support status with End-of-life dates.
Currently supported (bug + security fixes):
Security fixes only: