System versions
===============

Mailman system information is available through the System object, which
implements the ISystem interface.

    >>> from mailman.interfaces.system import ISystem
    >>> from mailman.core.system import system
    >>> from zope.interface.verify import verifyObject

    >>> verifyObject(ISystem, system)
    True

The Mailman version is available via the system object.

    >>> print system.mailman_version
    GNU Mailman ...

The Python version running underneath is also available via the system
object.

    # The entire python_version string is variable, so this is the best test
    # we can do.
    >>> import sys
    >>> system.python_version == sys.version
    True