We've always claimed that Mailman 2.1 will be compatible with Python versions back to and including Python 2.1. However, the Mailman 2.1.9 release inadvertently broke compatibility with Python 2.1. So as of Mailman 2.1.9 we're going to retroactively drop support for Python 2.1 and Python 2.2. For the rest of the Mailman 2.1 series we will officially support only Python 2.3 and newer.
There are several reasons for this, other than the accidental breakage in Mailman 2.1.9:
- Python 2.1 hasn't been officially supported by the Python Software Foundation for years, with the last official release of Python 2.1.3 in April 2002.
- Python 2.2 was a radical release, mostly notably with the unification of types and classes. The new features introduced in Python 2.2 weren't stabilized until Python 2.3 and it is not recommended to use Python 2.2 at all. Python 2.2.3 was released in May 2003 and is no longer officially supported by the PSF.
Python 2.3 is also no longer being officially support by the PSF, and the last release in this series was Python 2.3.5 in February 2005. However, many major Linux distributions (e.g. RedHat Enterprise Linux 4 and Mac OS X 10.4 (a.k.a. Tiger) come with Python 2.3.
Another reason is that I often develop on Mac OS X and I can't actually get Python earlier than 2.3 to even build on my dev boxes, which makes testing pretty difficult.
Also see DOC/Installation requirements.