You can find more info about Python Natural Language Toolkit (NLTK) sentence level tokenizer on their wiki.
From your command line:
$ python
>>> import nltk
>>> sent_tokenizer = nltk.tokenize.PunktSentenceTokenizer()
>>> text = "This is a sentence. This is another sentence. More sentences are better!"
>>> sent_tokenizer.tokenize(text)
Out[4]:
['This is a sentence.',
'This is another sentence.',
'More sentences are better!']