@classmethod
def get_currency(klass, text):
    u"""
        >>> Currency.get_currency(u'42')
        None
        >>> Currency.get_currency(u'42 €')
        u'EUR'
        >>> Currency.get_currency(u'$42')
        u'USD'
        >>> Currency.get_currency(u'42.000,00€')
        u'EUR'
        >>> Currency.get_currency(u'$42 USD')
        u'USD'
        >>> Currency.get_currency(u'%42 USD')
        u'USD'
        >>> Currency.get_currency(u'US1D')
        None
        """
    curtexts = klass.EXTRACTOR.sub(' ', text.upper()).split()
    for currency, symbols in klass.CURRENCIES.items():
        for curtext in curtexts:
            if curtext == currency:
                return currency
            for symbol in symbols:
                if curtext == symbol:
                    return currency
    return None
