Python, making List of List of Tuple

my intention was to Prepare a training Data for the HMM tagger, for a local corpus (ethiopic)

the tagger has the following syntax:

tagger = trainer.train_supervised(tr_data)

where the parameter tr_data should be in the format of List of List of Tuples

like, tr_data = [sent1, sent2,...]
where sent = [tuple1, tuple2],
and tuple = (word1, tag1), (word2, tag2),...

i have tried the following script, but all i get is just list of tuples, rather than list of list of tuples.

here is my script


import nltk;

wordtag = open("B:\Python\Teacher\Amharic_tagged_tr_corpus.txt","r");
wordtag = wordtag.readlines();
wordTagList = [];

for wt in wordtag:
wordTagList.append(wt.strip("\n"));

sentlist = [];

for w in wordTagList:
sentlist.append(nltk.sent_tokenize(w));

tuple = [];
for s in sentlist:
for w in s:
tuple.append(nltk.word_tokenize(w));

tuplelist = [];
for t in tuple:
for w in t:
tuplelist.append(nltk.tag.str2tuple(w));

print tuplelis[0:3] will list list of tuples like, [(w,t),(w,t),...] , where what i need is [[(w,t), (w,t), ...],[],..]

any help?