Unicode name questions

[Skip Montanaro]

I'm trying to build a dictionary that maps HTML entities to the appropriate
Unicode string literals.  I found three entities whose purported Unicode
names, when used, generate 

    UnicodeError: Unicode-Escape decoding error: unknown Unicode character name

They are:

    _entities['Λ'] = u"\N{GREEK CAPITAL LETTER LAMBDA}"
    _entities['λ'] = u"\N{GREEK SMALL LETTER LAMBDA}"
    _entities['ϑ'] = u"\N{GREEK SMALL LETTER THETA SYMBOL}"

Have I got the names wrong or are there some missing character names in
Python's Unicode support?

Thanks,

-- 
Skip Montanaro (skip at pobox.com - http://www.mojam.com/)