在尝试抓取Google链接时，我不明白这个错误

Question

我对Python很陌生，所以我很抱歉这是一个简单的问题，我正在尝试编写一个网络抓取工具，以便使用BeautifulSoup和Mechanize来搜索与网络相关的所有相关链接。

在报废时我收到的错误是：

Traceback (most recent call last):
  File "scrape.py", line 30, in <module>
    test.find_soup()
  File "scrape.py", line 23, in find_soup
    data = BS(self._launch()).read()
TypeError: 'NoneType' object is not callable

我不明白发生了什么事有人请向我解释我做错了什么？

代码：

from BeautifulSoup import BeautifulSoup as BS
import mechanize
import urlparse


class Initialize(object):

    def __init__(self, url, search):
        self.url = url
        self.search = search

    def _launch(self):
        search = mechanize.Browser()
        search.set_handle_robots(False)
        search.set_handle_equiv(False)
        search.addheaders = [('User-agent', 'Mozilla/5.0')]
        search.open(self.url)
        search.select_form(name="f")
        search.form["q"] = self.search
        return search.submit()

    def find_soup(self):
        data = BS(self._launch()).read()
        i = 0
        for link in data.select(".r a"):
            return "Relevant link [{}]: {}".format(i+1,
                                                   urlparse.urlparse(link["href"]).query["q"][0])

test = Initialize("https://google.com", "networking")
test.find_soup()