This pattern matches the name of a monthly file such as
'2005-09.xml'. Note that it will match
invalid month names such as '1999-00.xml'
and '2008-19.xml', but that is hardly
a world-shattering defect.
YYYY_MM_XML_PAT = re.compile (
r'[12]\d{3}' # Matches 1000-2999
r'\-' # Matches '-'
r'[01]\d' # Matches 00-19
r'\.' # Matches '.'
r'xml' # Matches 'xml'
r'$' ) # End-of line anchor: insure a complete match