automatization of web browsing with JavaScripts under python

You don't have to extract the javascript variable itself, just where it uses that variable. In this case it is placed in the href of the results back from the search.

There a bunch of different libraries you can use for automation. It depends on the level of automation you wish to see. In my case, I prefer to use selenium for these types of automation. Couple that with the core python module regex and you can create a basic example. I was able to write a quick mockup using selenium:

from selenium import webdriver
import re

url = "http://www.consultant.ru/search/?q=N+145-%D0%A4%D0%97+%D0%BE%D1%82+31.07.1998"
pattern = re.compile("n=(\d+)")
xpath = '//div[@id = "baseSrch"]//a'

browser = webdriver.Firefox()
page = browser.get(url)
elements = browser.find_elements_by_xpath(xpath)
browser.close()

for element in elements:
    match = re.search(pattern, element.get_attribute("href"))
    if match:
        print match.group(1)

Which yields:

160111

However this isn't the only way, you could also substitute this with urllib, requests, lxml, etc.. There are a bunch of different methods with which you can extract the information.