1def beginning(word):
 2    size = len(word)
 3    remainder = size % 3
 4
 5    if size == 0:
 6        return ''
 7    elif remainder == 2:
 8        index = int(size / 3) + 1
 9    else:
10        index = int(size / 3) 
11
12    return word[:index]
13    
14def middle(word):
15    size = len(word)
16    remainder = size % 3
17
18    if size == 1:
19       return word[0]
20    elif size == 2:
21       return ''
22    elif remainder in (0 , 1):
23       index = int(size / 3)
24       return word[index : size - index]
25    else:
26       index = int(size / 3)
27       return word[index + 1 : size - index - 1]
28
29def end(word):
30    size = len(word)
31    remainder = size % 3
32
33    if size <= 1:
34        return ''
35    elif remainder == 2:
36        index = int(size / 3) + 1
37    else:
38        index = int(size / 3) 
39
40    return word[size - index :]       
41
42def split_sentence(sentence):
43    words_list = sentence.split()
44    result_list=[]
45
46    for i in words_list:
47        result_list.append((beginning(i), middle(i), end(i)))
48        
49    return result_list
50
51# some test cases I checked:
52
53# print(beginning("nelina"), middle("nelina"), end("nelina"))
54# print( beginning("Пица"), middle("Пица"), end("пица"))
55# print(beginning("барабани"), middle("барабани"), end("барабани"))
56# print(beginning("Враца"), middle("Враца"),end("Враца"))
57# print(beginning("123456654321"), middle("1234567654321"), end("1234567654321"))
58# print(beginning("домашно"), middle("домашно"), end("домашно"))
59# print(beginning("aheloy"), middle("aheloy"), end("aheloy"))
60# print(beginning("шах"), middle("шах"), end("шах"))
61# print(beginning("пайтън"), middle("пайтън"), end("пайтън"))
62# print(beginning("pa"), middle("pa"), end("pa"))
63# print(beginning("p"), middle("p"), end("p"))
64# print(beginning(""), middle(""), end(""))
65# print(beginning("pa/ra"), middle("pa/ra"), end("pa/ra"))
66
67# print(split_sentence('Kазвам се Джон Сноу'))
68# print(split_sentence('аз купих домати и краставици от магазина'))
69# print(split_sentence('О'))
70# print(split_sentence('Ок'))