alvas@ubi:~$ python -m timeit -s "import nltk"
100000000 loops, best of 3: 0.0127 usec per loop
alvas@ubi:~$ python -m timeit -s "import nltk; from nltk import pos_tag, word_tokenize"
100000000 loops, best of 3: 0.012 usec per loop
alvas@ubi:~$ python -m timeit -s "import nltk; from nltk import pos_tag, word_tokenize; from nltk.stem import WordNetLemmatizer"
100000000 loops, best of 3: 0.0126 usec per loop