Converting an integer to Greek and Roman numerals
Your conversion routines make no sense.  I don't see why 45 should be ϜϜϜϜϜϜϜγ, as stated in your doctest.  I also get this clearly wrong result:

&gt;&gt;&gt; convert_init(1939, ROMAN_NUMERAL_TABLE)
'XLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXLXVIV'


Since you are using Unicode for the Greek numerals, I should be pedantic and point out that the Roman numerals should also use the appropriate Unicode characters.

The docstring would be better written as

def convert_init(number, convert_to=None):
    """
    Convert a number to a Greek or Roman numeral

    &gt;&gt;&gt; convert_init(45, convert_to=ROMAN_NUMERAL_TABLE)
    'XLV'
    """
    …


… since the print statement obscures the fact that you are returning a string.  (Based on just your docstring, it could also be returning some other kind of object, whose __str__ produces the desired output.)

What is convert_init?  Did you mean convert_int?

Your args = opts.parse_args() is not guarded by if __name__ == '__main__' as it should be.  You shouldn't need to cast int(args.greek) or int(args.roman), since argparse should take care of the type=int for you.