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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def lookup_symbol(self, symbol, as_of_date, fuzzy=False, country_code=None):
 """Lookup an equity by symbol. Parameters symbol : str The ticker symbol to resolve. as_of_date : datetime or None Look up the last owner of this symbol as of this datetime. If ``as_of_date`` is None, then this can only resolve the equity if exactly one equity has ever owned the ticker. fuzzy : bool, optional Should fuzzy symbol matching be used? Fuzzy symbol matching attempts to resolve differences in representations for shareclasses. For example, some people may represent the ``A`` shareclass of ``BRK`` as ``BRK.A``, where others could write ``BRK_A``. country_code : str or None, optional The country to limit searches to. If not provided, the search will span all countries which increases the likelihood of an ambiguous lookup. Returns ------- equity : Equity The equity that held ``symbol`` on the given ``as_of_date``, or the only equity to hold ``symbol`` if ``as_of_date`` is None. Raises ------ SymbolNotFound Raised when no equity has ever held the given symbol. MultipleSymbolsFound Raised when no ``as_of_date`` is given and more than one equity has held ``symbol``. This is also raised when ``fuzzy=True`` and there are multiple candidates for the given ``symbol`` on the ``as_of_date``. Also raised when no ``country_code`` is given and the symbol is ambiguous across multiple countries. """

        if symbol is None:
            raise TypeError("Cannot lookup asset for symbol of None for "
                            "as of date %s." % as_of_date)

        if fuzzy:
            f = self._lookup_symbol_fuzzy
            mapping = self._choose_fuzzy_symbol_ownership_map(country_code)
        else:
            f = self._lookup_symbol_strict
            mapping = self._choose_symbol_ownership_map(country_code)

        if mapping is None:
            raise SymbolNotFound(symbol=symbol)
        return f(
            mapping,
            country_code is None,
            symbol,
            as_of_date,
        )