Resource u'tokenizers/punkt/english.pickle' not found

My Code:

    tokenizer ='nltk:tokenizers/punkt/english.pickle')

ERROR Message:

    [ec2-user@ip-172-31-31-31 sentiment]$ python
    Traceback (most recent call last):
    File "", line 16, in <module>

        tokenizer ='nltk:tokenizers/punkt/english.pickle')

    File "/usr/lib/python2.6/site-packages/nltk/", line 774, in load

        opened_resource = _open(resource_url)

    File "/usr/lib/python2.6/site-packages/nltk/", line 888, in _open

        return find(path_, path + ['']).open()

    File "/usr/lib/python2.6/site-packages/nltk/", line 618, in find

        raise LookupError(resource_not_found)


    Resource u'tokenizers/punkt/english.pickle' not found.  Please
    use the NLTK Downloader to obtain the resource:


    Searched in:
    - '/home/ec2-user/nltk_data'
    - '/usr/share/nltk_data'
    - '/usr/local/share/nltk_data'
    - '/usr/lib/nltk_data'
    - '/usr/local/lib/nltk_data'
    - u''

I'm trying to run this program in Unix machine:

As per the error message, I logged into python shell from my unix machine then I used the below commands:

    import nltk

and then I downloaded all the available things using d- down loader and l- list options but still the problem persists.

I tried my best to find the solution in internet but I got the same solution what I did as I mentioned in my above steps.

I got the solution:

    import nltk

once the NLTK Downloader starts

d) Download l) List u) Update c) Config h) Help q) Quit

Downloader> d

Download which package (l=list; x=cancel)? Identifier> punkt