List linearization. Part 2.

The previous post I've talked about tricky list comprehension:
>>> ll = [[1,2,3], [4,5,6], [7,8]]
>>> l = [i for j in l for i in j]
>>> print l
... [1, 2, 3, 4, 5, 6, 7, 8]

But there are another pretty interesting solution for this task. It's based on built-in sum function:
>>> sum(ll)
TypeError: unsupported operand type(s) for +: 'int' and 'list'

Not working... But sum has optional param called `start` (which is 0 by default). So we could pass empty list, so every element in ll will be +'ed to it:
>>> print sum(ll, [])
... [1, 2, 3, 4, 5, 6, 7, 8]

Hooray! It works! And it's elegant. ;)

One more tricky thing I like in python

For example, I've got the list of iterable objects:
>>> l = [[1,2,3], [4,5,6], [7,8]]
And I need to get linear list of all elements in those iterables. Here's the trick, related to the list comprehension, I've learned couple of weeks ago:
>>> ll = [i for j in l for i in j]
>>> print ll
... [1, 2, 3, 4, 5, 6, 7, 8]

This constuction may be found a bit complicated at the first glance, but if we'll look at it, we'll get that that's similar to the following code:
>>> for j in l:
>>>     for i in j:
>>>         yield i