possibleStats = {
	'chromosome':args.chromosome,
	'type':args.type,
	'flag':args.flag,
	'tlen':args.tlen,
	'gc':args.gc
}
CHROMOSOME,TYPE,FLAG,TLEN,GC = False,False,False,False,False 	# create the variables which are set PER ROW of the file.
columns = []
for key,value in possibleStats.items():							# create a list of the variables used. we do this outside
	if value: columns.append(key.upper())	# of the main loop so it only needs to happen once per file.

for line in file:
	[... code that sets CHROMOSOME,TYPE,FLAG,TLEN and GC to some kind of value ]
	try:
		data[eval(columns)] += 1
		#data[(CHROMOSOME,TYPE,FLAGS,TLEN,GC)] += 1
	except KeyError:
		data[eval(columns)] = 1
		#data[(CHROMOSOME,TYPE,FLAGS,TLEN)] = 1