code: def fasta(self, loc, mask='mask'):
          
          
          l = libdna.parse_loc(loc)
          
          print('>{}'.format(l))
          print(self.dna(l, mask=mask))
docs: 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.