In doing this, I also learned that you could not take the len of a groupby object :-)

The code:

(Note: I would like to make this available under the Python License version 2.4.2)

''' \

Length sorts. From https://prof.ti.bfh.ch/hew1/informatik3/prolog/p-99/ P28

A code kata

Answer in Python (C) Donald 'Paddy' McCarthy, Feb. 23, 2008

'''

from itertools import groupbydeflength_sort(lst):

''' \

Sort a list-of-lists on sub-list length

Example

>>> l = [['a','b','c'],['d','e'],['f','g','h'],['d','e'],['i','j','k','l'],['m','n'],['o']]

>>> length_sort(l)

[['o'], ['d', 'e'], ['d', 'e'], ['m', 'n'], ['a', 'b', 'c'], ['f', 'g', 'h'], ['i', 'j', 'k', 'l']]

'''

returnsorted(lst, key=len)deflength_freq_sort(lst):

''' \

Sort a list-of-lists on frequency of sub-lists length

Example

>>> l = [['a','b','c'],['d','e'],['f','g','h'],['d','e'],['i','j','k','l'],['m','n'],['o']]

>>> length_freq_sort(l)

[['i', 'j', 'k', 'l'], ['o'], ['a', 'b', 'c'], ['f', 'g', 'h'], ['d', 'e'], ['d', 'e'], ['m', 'n']]

'''

## Comments give example working out

# >>> lst = [['a','b','c'],['d','e'],['f','g','h'],['d','e'],['i','j','k','l'],['m','n'],['o']]

lengths = sorted(len(x)forxinlst)

# >>> lengths

# [1, 2, 2, 2, 3, 3, 4]

# >>> [(a,len(list(b))) for a,b in groupby(lengths)]

# [(1, 1), (2, 3), (3, 2), (4, 1)]

# >>> dict([(a,len(list(b))) for a,b in groupby(lengths)])

# {1: 1, 2: 3, 3: 2, 4: 1}

len2freq = dict([(a,len(list(b)))fora,bingroupby(lengths)])

returnsorted(lst, key=lambdax: len2freq[len(x)])