Как нажать на кнопку на сайте?

from grab import Grab
import logging
 
 
logging.basicConfig(level=logging.DEBUG)
 
g=Grab(log_file='out.html')
g.go('http://ya.ru//')
g.set_input('text', '22')
 
g.submit(submit_name='submit')

g.set_input('text', '22')

TypeError: object of type 'InputGetter' has no len()

from twill.commands import *
 
 
go("http://www.google.com")
showforms()
 
 
fv('1','q', 'dog')
 
submit()

g.set_input('text', '')

  File "C:\Python27\lib\site-packages\grab-0.4.8-py2.7.egg\grab\ext\form.py", line 238, in submit
    post = self.form_fields()
  File "C:\Python27\lib\site-packages\grab-0.4.8-py2.7.egg\grab\ext\form.py", line 320, in form_fields
    fields = dict(self.form.fields)
  File "C:\Python27\lib\site-packages\grab-0.4.8-py2.7.egg\grab\ext\form.py", line 95, in form
    forms = [(idx, len(x.fields)) for idx, x in enumerate(self.tree.forms)]
  File "C:\Python27\lib\site-packages\lxml\html\__init__.py", line 931, in __len__
    return len(self.inputs)
TypeError: object of type 'InputGetter' has no len()
>>>

# -*- coding: utf-8 -*-
#!/usr/bin/env python
 
import mechanize
import sys
 
browser = mechanize.Browser()
 
browser.set_handle_robots(False)
browser.addheaders = [('User-agent', 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.62 Safari/537.36')]
 
browser.open('http://ya.ru')
browser.select_form(nr=0)
 
browser['text'] = 'answer to the ultimate question of life, the universe, and everything'
 
browser.submit()
 
def filter_answers(link):
    attrs = link.attrs
    klass = None
    for attr in attrs:
        if attr[0] == 'class':
            klass = attr[1]
            break
 
    return klass and klass == 'b-serp-item__title-link'
 
for link in browser.links(predicate=filter_answers):
    print link.url

g.set_input_by_number(3,'260')

g.set_input_by_xpath('//div[@class="btn-group radio-list "]','3974')

g.set_input_by_xpath('btn',3974)

r=g.xpath('//button[@value="3974"]')
g.submit(submit_name=r)