Python 网络爬虫，我可以从 for 循环调用函数吗？

Question

所以我试着编写这个网络爬虫，让它获取所有标题 URL 链接，然后去寻找所有章节 URL 链接，然后从章节链接找到所有章节链接等。

问题是，我在这个 https://github.com/buckyroberts/Source-Code-from-Tutorials/blob/master/Python/27_workingsolution_python.py 教程中看到，作者能够在定义第二个函数之前调用它。这真的很令人困惑。

我尝试了类似的方法，但得到的名字 "leveltwo" is not defined，正如预期的那样。我的问题是，如何使用从前一个函数获得的链接将其用作第二个函数的参数等等。

我的代码：

import requests
from bs4 import BeautifulSoup, SoupStrainer
import re


######################################Titles###############################
def levelone(url):
 r = requests.get(url)
 for links in BeautifulSoup((r.content),"html.parser",parse_only=SoupStrainer('a')):
    if links.has_attr('href'):
        if 'title' in links['href']:
          titlelinks = "http://law.justia.com" + links.get('href')
          # titlelinks = "\n" + str(titlelinks)  
          leveltwo(titlelinks) 
          # print (titlelinks)


base_url = "http://law.justia.com/codes/alabama/2015/"
levelone(base_url)


########################################Chapters##########################
def leveltwo(item_url):
 r = requests.get(item_url)
 for sublinks in BeautifulSoup((r.content),"html.parser",parse_only=SoupStrainer('a')):
  if sublinks.has_attr('href'):
   if 'chapt' in sublinks['href']:
         chapterlinks = "http://law.justia.com" + sublinks.get('href')
         # chapterlinks = "\n" + str(chapterlinks)  

         levelthree(chapterlinks)
         # print (chapterlinks)

# leveltwo(titlelinks) ### I tried call the function right here, but titlelinks is not defined.

########################################Sections##########################
def levelthree(item2_url):
 r = requests.get(item2_url)
 for sectionlinks in BeautifulSoup((r.content),"html.parser",parse_only=SoupStrainer('a')):
  if sectionlinks.has_attr('href'):
   if 'section' in sectionlinks['href']:
         href = "http://law.justia.com" + sectionlinks.get('href')
         href = "\n" + str(href)
         print (href)

Answer 1

先定义函数再调用

import requests
from bs4 import BeautifulSoup, SoupStrainer
import re

########################################Sections##########################
def levelthree(item2_url):
 r = requests.get(item2_url)
 for sectionlinks in BeautifulSoup((r.content),"html.parser",parse_only=SoupStrainer('a')):
  if sectionlinks.has_attr('href'):
   if 'section' in sectionlinks['href']:
         href = "http://law.justia.com" + sectionlinks.get('href')
         href = "\n" + str(href)
         print (href)

########################################Chapters##########################
def leveltwo(item_url):
 r = requests.get(item_url)
 for sublinks in BeautifulSoup((r.content),"html.parser",parse_only=SoupStrainer('a')):
  if sublinks.has_attr('href'):
   if 'chapt' in sublinks['href']:
         chapterlinks = "http://law.justia.com" + sublinks.get('href')
         # chapterlinks = "\n" + str(chapterlinks)  

         levelthree(chapterlinks)
         # print (chapterlinks)

######################################Titles###############################
def levelone(url):
 r = requests.get(url)
 for links in BeautifulSoup((r.content),"html.parser",parse_only=SoupStrainer('a')):
    if links.has_attr('href'):
        if 'title' in links['href']:
          titlelinks = "http://law.justia.com" + links.get('href')
          # titlelinks = "\n" + str(titlelinks)  
          leveltwo(titlelinks) 
          # print (titlelinks)

###########################################################################
base_url = "http://law.justia.com/codes/alabama/2015/"
levelone(base_url)

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