How To Build Scrapy Environment

[YetToCome]

I have already install Twisted, zope.interface, w3lib, libxml2, etc,but it still can not be built,here is the error message:

Traceback (most recent call last):
  File "C:\Python27\lib\runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "C:\Python27\lib\runpy.py", line 72, in _run_code
    exec code in run_globals
  File "C:\Python27\lib\site-packages\scrapy\cmdline.py", line 167, in <module>
    execute()
  File "C:\Python27\lib\site-packages\scrapy\cmdline.py", line 142, in execute
    _run_print_help(parser, _run_command, cmd, args, opts)
  File "C:\Python27\lib\site-packages\scrapy\cmdline.py", line 88, in _run_print
_help
    func(*a, **kw)
  File "C:\Python27\lib\site-packages\scrapy\cmdline.py", line 149, in _run_comm
and
    cmd.run(args, opts)
  File "C:\Python27\lib\site-packages\scrapy\commands\crawl.py", line 47, in run
    crawler = self.crawler_process.create_crawler()
  File "C:\Python27\lib\site-packages\scrapy\crawler.py", line 142, in create_cr
awler
    self.crawlers[name] = Crawler(self.settings)
  File "C:\Python27\lib\site-packages\scrapy\crawler.py", line 23, in __init__
    self.spiders = spman_cls.from_crawler(self)
  File "C:\Python27\lib\site-packages\scrapy\spidermanager.py", line 35, in from
_crawler
    sm = cls.from_settings(crawler.settings)
  File "C:\Python27\lib\site-packages\scrapy\spidermanager.py", line 31, in from
_settings
    return cls(settings.getlist('SPIDER_MODULES'))
  File "C:\Python27\lib\site-packages\scrapy\spidermanager.py", line 22, in __in
it__
    for module in walk_modules(name):
  File "C:\Python27\lib\site-packages\scrapy\utils\misc.py", line 66, in walk_mo
dules
    submod = __import__(fullpath, {}, {}, [''])
  File "blog_crawl\spiders\dmoz_spider.py", line 1, in <module>
    class DmozSpider(BaseSpider):
NameError: name 'BaseSpider' is not defined

someone tells me why, pls