This is perhaps the coolest idiom of Python I have seen yet. Thanks

to Clint for stopping by my office for a Python versus Perl versus PHP smackdown that got me thinking.

This is a great way to sort a list of tuples on the second key:

>>> import operator >>> a = [ (1,'z'), (2, 'x'), (3, 'y') ] >>> a.sort(key=operator.itemgetter(1)) >>> a [(2, 'x'), (3, 'y'), (1, 'z')] >>>

Pretty clever. The method name could be a bit shorter :)

Here is an operator free version using lamda

>>> a.sort(key=lambda x: x[1]) >>> a [(2, 'x'), (3, 'y'), (1, 'z')]

And here is one that uses the second entry and the first entry:

>>> a.sort(key=lambda x: (x[1], x[0]) ) >>> a [(2, 'x'), (3, 'y'), (1, 'z')]

And then the most super-duper fun one of all – sorting a dictionary:

>>> a = { "a": 9, "b" : 8, "c" : 7 } >>> b = sorted(a.items()) # Sort by key >>> b [('a', 9), ('b', 8), ('c', 7)] >>> >>> c = sorted(a.items(),key=lambda x: x[1]) # By value >>> c [('c', 7), ('b', 8), ('a', 9)] >>> c = sorted(a.items(),key=lambda x: x[1], reverse=True) # By Value Backwards >>> c [('a', 9), ('b', 8), ('c', 7)] >>> d = sorted(a.items(),key=lambda x: (x[1], x[0]), reverse=True) # Value then Key >>> d [('a', 9), ('b', 8), ('c', 7)] >>>

Time to go put this in my Python book in Chapter 10 (www.py4inf.com). Too bad it did not make it into version 0.0.2 printed copies – but it will make it into the Chapter 10 lecture slides!

More fun tricks at: http://wiki.python.org/moin/HowTo/Sorting