[ Python 常見問題 ] Sorting a dict with tuples as values

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Question 
I have a structure that looks like this: 

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1. {'key_info':(rank,raw_data1,raw_data2),'key_info2':....}  

basically i need back a list of the keys in a sorted order, that is sorted based on the specific field in the tuple. 

How-To 
With help of API:sorted, you can do it this way: 

>>> test_dict = {}
>>> test_dict['John'] = (18, 'Taiwan')
>>> test_dict['Ken'] = (22, 'American')
>>> test_dict['Peter'] = (16, 'Japan')
>>> test_dict['Mary'] = (30, 'China')
>>> test_dict
{'Ken': (22, 'American'), 'John': (18, 'Taiwan'), 'Peter': (16, 'Japan'), 'Mary': (30, 'China')}
>>> sorted(test_dict.keys(), key=lambda k: test_dict[k][0], reverse=True) # Sorting with age in descending order
['Mary', 'Ken', 'John', 'Peter']
>>> sorted(test_dict.keys(), key=lambda k: test_dict[k][1]) # Sorting with country name in ascending order
['Ken', 'Mary', 'Peter', 'John']
>>> test_dict['Winson'] = (29, 'Canada')
>>> test_dict['Jacy'] = (24, 'China')
>>> sorted(test_dict.keys(), key=lambda k: (test_dict[k][1], test_dict[k][0])) # Sorting with country, then age in ascending order
['Ken', 'Winson', 'Jacy', 'Mary', 'Peter', 'John'] # Jacy=(24, 'China'); Mary=(30, 'China')

Supplement 
* Python Doc - Sorting HOW TO 
* Sort a list by multiple attributes?