s1 = 'Foo'
s2 = 'Boo'
s3 = 'Foo'
s4 = 'Duh'
s = "We have a collection of types {}."
lst = [s1,s2,s3,s4]
fin = []
for x in lst:
	if x not in fin:
		fin.append(x)
print(s.format(", ".join(fin)))