Partition a list into N chunks of nearly equal size.

chunk.py

def chunk(L, n): 
    '''
    Partition L into n chunks using every item in L and 
    such that the resulting chunks differ in size by at 
    most one element.
    
    >>> L = ['a', 'b', 'c', 'd']
    ['a', 'b', 'c', 'd']
    >>> chunk(L, 2)
    [['a', 'b'], ['c', 'd']]
    >>> chunk(L, 3)
    [['a'], ['b', 'c'], ['d']]
    >>> chunk(L, 4)
    [['a'], ['b'], ['c'], ['d']]
    >>> chunk(L, 5)
    [['a'], ['b'], [], ['c'], ['d']]

    '''
    size = len(L) / float(n) 
    I = lambda i: int(round(i))
    return [ L[I(size*i):I(size*(i+1))] for i in xrange(n) ]

parts.py

def parts(L, n): 
    '''
    Partition L into n parts using every item in L
    and such that the resulting chunks differ in size
    by at most one element.

    HT to [Mark Dickinson](http://stackoverflow.com/a/2660138/546630).
    
    >>> L = ['a', 'b', 'c', 'd'] 
    ['a', 'b', 'c', 'd']
    >>> parts(L, 2) 
    [['a', 'b'], ['c', 'd']]
    >>> parts(L, 3)
    [['a', 'b'], ['c'], ['d']]
    >>> parts(L, 4)
    [['a'], ['b'], ['c'], ['d']]
    >>> parts(L, 5)
    [['a'], ['b'], ['c'], ['d'], []]

    '''
    q, r = divmod(len(L), n)
    I = [q*i + min(i, r) for i in xrange(n+1)]
    return [L[I[i]:I[i+1]] for i in xrange(n)]