from collections import defaultdict, Counter
d1 = Counter()
d2 = defaultdict(set)
# count appearence of entries
for x in nameList:
d1[x] += 1
d2[x.lower()].add(x)
# dupes are
for k,v in d1.iteritems():
if v>1: print k
# different appearance of name
for k,v in d2.iteritems():
if len(v) > 1: print k
If you have a …long… list, take a look at bloom filter.