code: def getNucleotideCodon(sequence, x1) :
  	
  
  	if x1 < 0 or x1 >= len(sequence) :
  		return None
  
  	p = x1%3
  	if p == 0 :
  		return (sequence[x1: x1+3], 0)
  	elif p ==1 :
  		return (sequence[x1-1: x1+2], 1)
  	elif p == 2 :
  		return (sequence[x1-2: x1+1], 2)
docs: Returns the entire codon of the nucleotide at pos x1 in sequence, 
  	and the position of that nocleotide in the codon in a tuple