Python: break a list into pieces of a certain size and fill in the remainder

Question

I want to split my list into lines with the same number of columns, I'm looking for the best (most elegant / pythonic) way to achieve this:

>>> split.split_size([1,2,3], 5, 0) [[1, 2, 3, 0, 0]] >>> split.split_size([1,2,3,4,5], 5, 0) [[1, 2, 3, 4, 5]] >>> split.split_size([1,2,3,4,5,6], 5, 0) [[1, 2, 3, 4, 5], [6, 0, 0, 0, 0]] >>> split.split_size([1,2,3,4,5,6,7], 5, 0) [[1, 2, 3, 4, 5], [6, 7, 0, 0, 0]] 

What I came up with so far:

 def split_size(l, size, fillup): """ splits list into chunks of defined size, fills up last chunk with fillup if below size """ # len(l) % size or size # does ie size=5: 3->2, 4->1, 5->0 stack = l + [fillup] * (size - (len(l) % size or size)) result = [] while len(stack) > 0: result.append(stack[:5]) del stack[:5] return result 

I am sure that there should be some more reasonable solutions. Especially for the “reverse mod” part: len (l)% size or size should be a more readable way to do this, no?

Answer 1

an itertools recipe called grouper does what you want:

 def grouper(n, iterable, fillvalue=None): "grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx" args = [iter(iterable)] * n return izip_longest(fillvalue=fillvalue, *args)