def add_flanking_seqs(self, ref_seq, new_start, new_end):
if new_start > self.POS or new_end < self.ref_end_pos():<EOL><INDENT>raise Error('<STR_LIT>' + str(new_start) + '<STR_LIT>' + str(new_end) + '<STR_LIT>' + str(self))<EOL><DEDENT>new_start_nucleotides = ref_seq[new_start:self.POS]<EOL>new_end_nucleotodes = ref_seq[self.ref_end_pos() + <NUM_LIT:1>:new_end + <NUM_LIT:1>]<EOL>self.POS = new_start<EOL>self.REF = new_start_nucleotides + self.REF + new_end_nucleotodes<EOL>self.ALT = [new_start_nucleotides + x + new_end_nucleotodes for x in self.ALT]<EOL>
Adds new_start many nucleotides at the start, and new_end many nucleotides
        at the end from the appropriate nucleotides in reference sequence ref_seq.