Prints a fasta representation of a sequence.
        
        Parameters
        ----------
        l : tuple (str, int, int)
            location chr, start, and end
        mask : str, optional
            Either 'upper', 'lower', or 'n'. If 'lower', poor quality bases 
            will be converted to lowercase.

def fasta(self, loc, mask='mask'):
        """
        Prints a fasta representation of a sequence.
        
        Parameters
        ----------
        l : tuple (str, int, int)
            location chr, start, and end
        mask : str, optional
            Either 'upper', 'lower', or 'n'. If 'lower', poor quality bases 
            will be converted to lowercase.
        """
        
        l = libdna.parse_loc(loc)
        
        print('>{}'.format(l))
        print(self.dna(l, mask=mask))