how to tick a checkbox using robobrowser

i'm trying to tick a checkbox on the book which i issued from my college library so ,after doing the login, when i try to select the form and put the value to 1 it gives me a type error

here is my code for ticking.

box = browser.get_form(action="./selectedBooks")
box['selectedforRenewal'].value = '1'
browser.submit_form(box)
browser.parsed

here is the sourcecode.

 <form action="./selectedBooks" method="get" id="form1" target="nidhi">
 <input type="checkbox" name="selectedforRenewal" value="0">

and the traceback i'm getting.

 box['selectedforRenewal'].value = '1'
    TypeError: 'NoneType' object is not subscriptable

any help with that..