Chunk and slice operations on lists in Python

chunks_slice.py

from itertools import izip_longest
from string import lowercase


def chunk(s, size):
    '''
    Separates sequence into chunks of given size.
    
    >>> chunk('helloworld', 3)
    ['hel', 'low', 'orl', 'd']
    
    >>> chunk(range(20,30), 4)
    [[20, 21, 22, 23], [24, 25, 26, 27], [28, 29]]
    '''
    
    chunks = len(s) // size if len(s) % size == 0 else len(s) // size + 1
    return [s[i*size:i*size+size] for i in range(chunks)]


def chunk2(s, size, fillval=None):
    '''
    Returns iterator that will give a tuple of chunk elements on each iteration.
    
    Optional argument fillval will be used to fill in last chunk.
    
    >>> chunk2('helloworld', 3).next()
    ('h', 'e', 'l')
    
    >>> chunk2([1, 2], 3, fillval=0).next()
    (1, 2, 0)
    '''
    
    return izip_longest(*[iter(s)]*size, fillvalue=fillval)


def slicer(s, size, jump=1):
    '''
    Return slices of sequence with specified size and jump.
    
    >>> slicer('12345678', 3)
    ['123', '234', '345', '456', '567', '678']
    
    >>> slicer('hello', 4)
    ['hell', 'ello']
    '''
    
    newsize = len(s) - size + 1
    return [s[i:i+size] for i in range(0, newsize, jump)]