def strange_sort(items):
    unique = sorted(set(items))
    return [unique[i % len(unique)] for i in range(len(items))]
 
items = [1, 2, 2, 2, 2, 1, 1, 1, 3, 3, 3, 3]
print strange_sort(items)  # [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3]

from collections import Counter
 
def strange_sort(items):
    count = Counter(items)
    unique = sorted(count.keys())
    result = []
    while count:
        for item in unique:
            count[item] -= 1
            if count[item] < 0:
                del count[item]
            else:
                result.append(item)
    return result
 
items = [1, 1, 1, 1, 1, 2, 2, 2, 2, 1, 1, 1, 3, 3, 3, 3]
print strange_sort(items)  # [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 1, 1, 1]

>>> date = ['aaa', 'ddd', 'ddd', 'ddd', 'ddd', 'aaa', 'aaa', 'aaa', 'ccc', 'ccc', 'ccc', 'ccc']
>>> 
>>> def f(lst):
...     out = []
...     uni = set()
...     for i in lst:
...         if i not in uni:
...             uni.add(i)
...             out.append(i)
...     return len(lst) // len(out) * out
... 
>>> print(f(date))
['aaa', 'ddd', 'ccc', 'aaa', 'ddd', 'ccc', 'aaa', 'ddd', 'ccc', 'aaa', 'ddd', 'ccc']
>>>

>>> from itertools import chain, izip_longest, groupby
>>> date = ['aaa', 'ddd', 'aaa', 'aaa', 'aaa',  'ccc', 'ccc']
>>> filter(None, chain.from_iterable(izip_longest(*(list(x[1]) for x in groupby(sorted(date))))))
['aaa', 'ccc', 'ddd', 'aaa', 'ccc', 'aaa', 'aaa'