def is_snp(self):
nucleotides = {'<STR_LIT:A>', '<STR_LIT:C>', '<STR_LIT>', '<STR_LIT:T>'}<EOL>return len(self.REF) == <NUM_LIT:1> and self.REF in nucleotides and set(self.ALT).issubset(nucleotides)<EOL>
Returns true iff this variant is a SNP