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

My Code:

import nltk.data
tokenizer = nltk.data.load('nltk:tokenizers/punkt/english.pickle')

ERROR Message:

[ec2-user@ip-172-31-31-31 sentiment]$ python mapper_local_v1.0.py
Traceback (most recent call last):
File "mapper_local_v1.0.py", line 16, in <module>

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

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

    opened_resource = _open(resource_url)

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

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

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

    raise LookupError(resource_not_found)

LookupError:

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

    >>>nltk.download()

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
nltk.download()

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
nltk.download()

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