NameError: 全局名称'NAME'未定义

Question

我最近在做一个小的网页抓取工具，感觉自己在变量或函数的作用域上可能搞错了。每当我试着把一些功能拆分成单独的函数时，就会出现NameError: global name 'NAME' is not defined的错误。我发现很多人也遇到类似的问题，但大家的情况各不相同，我就是搞不明白到底是怎么回事。

import urllib2, sys, urlparse, httplib, imageInfo
from BeautifulSoup import BeautifulSoup
from collections import deque

global visited_pages
visited_pages = []
global visit_queue
visit_queue = deque([])
global motorcycle_pages
motorcycle_pages = []
global motorcycle_pics
motorcycle_pics = []

global count 
count = 0

def scrapePages(url):
    #variables
    max_count = 20
    pic_num = 20

    #decide how long it should go on...
    global count
    if count >= max_count:
        return

    #this is all of the links that have been scraped
    the_links = []

    soup = soupify_url(url)

    #find all the links on the page
    for tag in soup.findAll('a'):
        the_links.append(tag.get('href'))


    visited_pages.append(url)
    count = count + 1
    print 'number of pages visited'
    print count

    links_to_visit = the_links
#    print 'links to visit'
#    print links_to_visit

    for link in links_to_visit:
        if link not in visited_pages:
            visit_queue.append(link)
    print 'visit queue'
    print visit_queue

    while visit_queue:
        link = visit_queue.pop()
        print link
        scrapePages(link)

    print '***done***'


the_url = 'http://www.reddit.com/r/motorcycles'
#call the function
scrapePages(the_url)


def soupify_url(url):
    try:
        html = urllib2.urlopen(url).read()
    except urllib2.URLError:
        return 
    except ValueError:
        return
    except httplib.InvalidURL:
        return
    except httplib.BadStatusLine:
        return

    return BeautifulSoup.BeautifulSoup(html) 

这是我的错误追踪信息：

Traceback (most recent call last):
  File "C:\Users\clifgray\Desktop\Mis Cosas\Programming\appengine\web_scraping\src\test.py", line 68, in <module>
    scrapePages(the_url)
  File "C:\Users\clifgray\Desktop\Mis Cosas\Programming\appengine\web_scraping\src\test.py", line 36, in scrapePages
    soup = soupify_url(url)
NameError: global name 'soupify_url' is not defined

Answer 1

把你的主要代码移动一下：

the_url = 'http://www.reddit.com/r/motorcycles'
#call the function
scrapePages(the_url)

也就是把它放到你定义了 soupify_url 之后，也就是文件的底部。

Python 在读取的时候，发现 scrapePages() 这个函数已经定义了，然后它尝试去调用它；但是 scrapePages() 里面又想调用一个叫 soupify_url() 的函数，而这个函数还没有定义，所以你就会看到一个错误：

NameError: global name 'soupify_url' is not defined

记住这个规则：所有的函数必须在任何实际执行的代码之前定义

如果你把调用 scrapePages() 的主要代码移动到 soupify_url() 定义之后，所有的东西都会被定义好，这样就能解决你的错误了。