#!/usr/bin/env python

import urllib2
import re,sys

def pmid2doi(pmid):
   url = "http://www.ncbi.nlm.nih.gov/pubmed/%s?dopt=MEDLINE" % pmid
   r = re.compile('AID - (10.\d+/.+?) \[doi\]')
   response = urllib2.urlopen(url)
   if response.code == 200:
       s = response.read()
       m = r.search(s)
       return m.group(1)
   else:
       return "error: %d" % response.code

if __name__ == '__main__':
   if len(sys.argv) == 2:
       print pmid2doi(sys.argv[1])
   else:
       print "usage: %s [pmid]" % sys.argv[0]