Gets a Symbol based on name, which is expected to exist. 
        
        Parameters
        ----------
        symbol : str or Symbol
        
        Returns
        -------
        Symbol
        
        Raises
        ------
        Exception
            If it does not exist. Use .try_to_get(), 
            if the symbol may or may not exist.

def get(self, symbol):
        """ Gets a Symbol based on name, which is expected to exist. 
        
        Parameters
        ----------
        symbol : str or Symbol
        
        Returns
        -------
        Symbol
        
        Raises
        ------
        Exception
            If it does not exist. Use .try_to_get(), 
            if the symbol may or may not exist.
        """
        syms = self.try_to_get(symbol)
        if syms is None:
            raise Exception("Symbol {} does not exist".format(symbol))
        else:
            return syms