No, you should not stay on 11.04. It has been End of Life for support since October 2012. If you want any support at all, you need to upgrade, at least to 12.04 (which will be supported for three more years).
Also, even newer versions of of Ubuntu are including Python 3.x by default, with a goal of removing Python 2.x from the default install completely.
You may have issues with running your code under a newer version of Python 3.x, but should in general have no problems. You should also, as a developer, be prepared to deal with any such issues, regardless of what version of Ubuntu you are on. Any library you're using, or Python itself, could have a bug which your code depends on behaviorally, and if that bug is fixed, could cause your program to behave different from how you were expecting it to previously.