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mac_roman is an obsolete encoding from Mac OS 9 days; it is seldom seen on modern OS X systems. But it is often the fallback encoding set in ~/.CFUserTextEncoding if the LANG or a LC_* environment variable is not set (see, for example, http://superuser.com/questions/82123/mac-whats-cfusertextencoding-for). If you run a terminal session using Terminal.app, the LANG environment variable is usually set for you to an appropriate modern value, like 'en_US.UTF-8' in the US locale; this is controlled by a Terminal.app preference; other terminal apps like iTerm2 have something similar. But if you are using xterm with X11, xterm does not inject a LANG env variable. So, something like:
 python3.2 -c 'print("\u030a")'
may fail running under xterm with UnicodeEncodeError but will print the expected character when run under Terminal.app. I avoid those kinds of issues by explicitly setting LANG in my shell profile.
Let us know if that helps or, if not, how to reproduce your issue.