1. No error is caused, but trying to use the key pointing to the self reference
induces a warning about recursion, and stops immediately.

2. --- unique_count.py ---
d = {}
s = raw_input('Enter a name: ')
while s != '':
	if s in d:
		d[s] += 1
	else:
		d[s] = 1
	s = raw_input('Enter a name: ')
print d
--- end unique_count.py ---

3. --- string_dict.py ---
d = {}
s = raw_input('Enter a key:value pair> ')
while s != '':
	p = s.find(':')
	if p != -1:
		key = s[:p]
		value = s[p+1:]
	else:
		key = s
		value = None
	if key in d:
		print d[key]
	d[key] = value
	s = raw_input('Enter a key:value pair> ')

for k, v in d.items():
	print k, ":", v
--- end string_dict.py ---

4. --- guestbook.py ---
#!/usr/bin/python

database = {}

name = raw_input("Please enter your name: ")
while name != 'quit':
	if name == 'showcomments':
		for customer in database:
			print "%s\n\t%s"%(customer.capitalize(), database[customer.lower()])
	else:
		if name.lower() in database:
			print "Welcome back", name.capitalize()
			print "\t%s"%(database[name.lower()])
		comment = raw_input("Please enter your comment: ")
		if comment != "":
			database[name.lower()] = comment
	name = raw_input("Please enter your name: ")
--- end guestbook.py ---