Probably the interface changed and you need to do list(vocabulary1)[:50] or something like that.
>>> a=lambda x: x+2
>>> b = map(a, [1,2,3])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'map' object is not subscriptable
[3, 4, 5]
Big thanx! list(vocabulary1)[:50] - is working! The more general question i am interested: is there any docs on changes in syntax for Python 3 from Python 2 for NLTK? I afraid i will face other problems soon