So I have installed python 2.7 in cygwin and it runs without any problem. However, when I install new packages using cygwin's setup.exe, it will always select new version 2.6.8 for the python package by default, and if I don't switch back to 2.7.2, it will uninstall python 2.7 and install python 2.6. What's wrong with my cygwin? Is there any method to fix this problem?
Python 2.7.3 is currently experimental; the current supported version of Python for Cygwin is 2.6.8. Every time you run Cygwin's setup.exe, it sees that the version of Python you have installed isn't the latest supported version, and attempts to "upgrade" you to that version.
Noticing when you've intentionally selected an experimental version of a package, and not "upgrading" you to the stable version would be a nice feature for Cygwin's setup.exe to have. Sadly it doesn't; you just have to remember to change the install list every time you run setup.
(Although if you fancy it, I imagine such an enhancement to Cygwin's setup.exe would be gratefully received by the Cygwin community; it's an open source project and someone has to do the work!)
Jason Tishler, Cygwin's Python maintainer, announced the experimental package in December 2012. To quote his email:
I will update Cygwin to make 2.7.3-1 (or later) current on or about February 1, 2013.
That change will be announced on the "cygwin" and "cygwin-announce" mailing lists, if you fancy following them. Once that happens, the installer will work as you'd like it to.