Scraping aspx webpage with Python using BeautifulSoup

I am tryring to scrape this page: http://www.nitt.edu/prm/nitreg/ShowRes.aspx

Here is the code:

import urllib
from bs4 import BeautifulSoup

headers = {
    'Accept':'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
    'Origin': 'http://www.indiapost.gov.in',
    'User-Agent': 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.17 (KHTML, like Gecko)  Chrome/24.0.1312.57 Safari/537.17',
    'Content-Type': 'application/x-www-form-urlencoded',
    'Referer': 'http://www.nitt.edu/prm/nitreg/ShowRes.aspx',
    'Accept-Encoding': 'gzip,deflate,sdch',
    'Accept-Language': 'en-US,en;q=0.8',
    'Accept-Charset': 'ISO-8859-1,utf-8;q=0.7,*;q=0.3'
}

class MyOpener(urllib.FancyURLopener):
    version = 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.17 (KHTML, like Gecko) Chrome/24.0.1312.57 Safari/537.17'

myopener = MyOpener()
url = 'http://www.nitt.edu/prm/nitreg/ShowRes.aspx'
# first HTTP request without form data
f = myopener.open(url)
soup = BeautifulSoup(f)
# parse and retrieve two vital form values
viewstate = soup.findAll("input", {"type": "hidden", "name": "__VIEWSTATE"})
eventvalidation = soup.findAll("input", {"type": "hidden", "name": "__EVENTVALIDATION"})

print viewstate[0]['value']





formData = (
     ('__EVENTVALIDATION', eventvalidation),
    ('__VIEWSTATE', viewstate),
    ('__VIEWSTATEENCRYPTED',''),
    ('TextBox1', '106110006'),
    ('Button1', 'Show'),
)

encodedFields = urllib.urlencode(formData)
# second HTTP request with form data
f = myopener.open(url, encodedFields)

try:
    # actually we'd better use BeautifulSoup once again to
    # retrieve results(instead of writing out the whole HTML file)
    # Besides, since the result is split into multipages,
    # we need send more HTTP requests
    fout = open('tmp.html', 'w')
except:
    print('Could not open output file\n')
fout.writelines(f.readlines())
fout.close()

I keep getting a server error: Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[FormatException: Invalid character in a Base-64 string.]
   System.Convert.FromBase64String(String s) +0
   System.Web.UI.LosFormatter.Deserialize(String input) +25
   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +101

[HttpException (0x80004005): Invalid_Viewstate
    Client IP: 10.0.0.166
    Port: 51915
    User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.17 (KHTML, like Gecko) Chrome/24.0.1312.57 Safari/537.17
    ViewState: [<input name="__VIEWSTATE" type="hidden" value="dDwtMTM3NzI1MDM3O3Q8O2w8aTwxPjs+O2w8dDw7bDxpPDE+O2k8Mj47PjtsPHQ8cDxwPGw8VmlzaWJsZTs+O2w8bzxmPjs+Pjs+O2w8aTwxPjtpPDM+Oz47bDx0PDtsPGk8Mz47PjtsPHQ8O2w8aTwwPjs+O2w8dDw7bDxpPDE+Oz47bDx0PEAwPDs7Ozs7Ozs7Ozs+Ozs+Oz4+Oz4+Oz4+O3Q8cDxwPGw8VmlzaWJsZTs+O2w8bzxmPjs+Pjs+Ozs+Oz4+O3Q8O2w8aTw5PjtpPDExPjs+O2w8dDxwPHA8bDxWaXNpYmxlOz47bDxvPGY+Oz4+Oz47Oz47dDx0PHA8cDxsPFZpc2libGU7PjtsPG88Zj47Pj47Pjs7Pjs7Pjs+Pjs+Pjs+Pjs+zHrNhAd1tTLXbBUyAJRtS6omUc0="/>]
    Http-Referer: 
    Path: /prm/nitreg/ShowRes.aspx.]
   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +447
   System.Web.UI.Page.LoadPageViewState() +18
   System.Web.UI.Page.ProcessRequestMain() +447

Invalid character in a Base-64 string. What is the problem?

You are using the ViewState input object, not the value.

ViewState: [<input name="__VIEWSTATE" type="hidden" value="dDwtMTM3NzI1MDM3O3Q8O2w8aTwxPjs+O2w8dDw7bDxpPDE+O2k8Mj47PjtsPHQ8cDxwPGw8VmlzaWJsZTs+O2w8bzxmPjs+Pjs+O2w8aTwxPjtpPDM+Oz47bDx0PDtsPGk8Mz47PjtsPHQ8O2w8aTwwPjs+O2w8dDw7bDxpPDE+Oz47bDx0PEAwPDs7Ozs7Ozs7Ozs+Ozs+Oz4+Oz4+Oz4+O3Q8cDxwPGw8VmlzaWJsZTs+O2w8bzxmPjs+Pjs+Ozs+Oz4+O3Q8O2w8aTw5PjtpPDExPjs+O2w8dDxwPHA8bDxWaXNpYmxlOz47bDxvPGY+Oz4+Oz47Oz47dDx0PHA8cDxsPFZpc2libGU7PjtsPG88Zj47Pj47Pjs7Pjs7Pjs+Pjs+Pjs+Pjs+zHrNhAd1tTLXbBUyAJRtS6omUc0="/>]

Your formData should be:

formData = (
     ('__EVENTVALIDATION', eventvalidation[0]['value']),
    ('__VIEWSTATE', viewstate[0]['value']),
    ('__VIEWSTATEENCRYPTED',''),
    ('TextBox1', '106110006'),
    ('Button1', 'Show'),
)

Note your eventvalidation value has the same issue, I fixed it too.

EDIT: The __EVENTVALIDATION does not exist in that page. You can just remove __EVENTVALIDATION from formData.

formData = (
    ('__VIEWSTATE', viewstate[0]['value']),
    ('__VIEWSTATEENCRYPTED',''),
    ('TextBox1', '106110006'),
    ('Button1', 'Show'),
)