first-unique.py

import collections

def first_unique(some_list):
	dict_of_items = collections.OrderedDict()
	for item in some_list:
		if item in dict_of_items:
			dict_of_items[item] +=1
		else:
			dict_of_items[item] = 1
	for key in dict_of_items:
		if dict_of_items[key] == 1:
			return key
	return None

# Example input
# print first_unique('aabcc') # we can do this because a string is a list of characters.
# print first_unique([1,2,3,1,2])
# print first_unique(['aa','aa','bc','d'])

"""
 Code Breakdown
 --------------
 line 1: used for importing the ordered dictionary seen in line 4
 line 4: We need to use an ordered dictionary to remember what order we added items in,
         see http://bit.ly/1ANjFoJ or http://bit.ly/17F80Pc for more information regarding
         the OrderedDict collection.
 line 6: look at http://bit.ly/1xm0hKD for a interestingn conversation on if item in 
         dict_of_items vs. item in dict_of_items.keys()
 line 7: This increments the count of the number of instances we have seen of this item
 line 12: this halts the function once the first unique item is found.
 line 13: if no unique value is found return None
"""