Bi-directional Dictionary in Python

Here’s an quick function for creating a bi-directional dictionary in Python:

def bidict(d):
    d2 = d.copy()
    for k,v in d.items():
        if v in d2.keys():
            raise KeyError('Cannot create bidirectional dict.
' +
                           'Either d has a value that is the same as one of ' +
                           'its keys or multiple keys have the same value.')
        d2[v] = k
    return d2
hellos = {"Chinese" : "你好世界",
          "Dutch" : "Hello wereld",
          "English" : "Hello world",
          "French" : "Bonjour monde",
          "German" : "Hallo Welt",
          "Greek" : "γειά σου κόσμος",
          "Italian" : "Ciao mondo",
          "Japanese" : "こんにちは世界",
          "Korean" : "여보세요 세계",
          "Portuguese" : "Olá mundo",
          "Russian" : "Здравствулте мир",
          "Spanish" : "Hola mundo"}
bidict(hellos)

The new dict will look like this:

{'Bonjour monde': 'French',
 'Chinese': '你好世界',
 'Ciao mondo': 'Italian',
 'Dutch': 'Hello wereld',
 'English': 'Hello world',
 'French': 'Bonjour monde',
 'German': 'Hallo Welt',
 'Greek': 'γειά σου κόσμος',
 'Hallo Welt': 'German',
 'Hello wereld': 'Dutch',
 'Hello world': 'English',
 'Hola mundo': 'Spanish',
 'Italian': 'Ciao mondo',
 'Japanese': 'こんにちは世界',
 'Korean': '여보세요 세계',
 'Olá mundo': 'Portuguese',
 'Portuguese': 'Olá mundo',
 'Russian': 'Здравствулте мир',
 'Spanish': 'Hola mundo',
 'γειά σου κόσμος': 'Greek',
 'Здравствулте мир': 'Russian',
 'こんにちは世界': 'Japanese',
 '你好世界': 'Chinese',
 '여보세요 세계': 'Korean'}