为什么这会返回 NoneType？

Question

我正在尝试使用以下函数从 Wikipedia 中获取信息，但我遇到了 属性错误，因为函数调用返回 None。有人可以尝试解释为什么这会返回 None 吗？

import wikipedia as wp
import string

def add_section_info(search):
    HTML = wp.page(search).html().encode("UTF-8") #gets HTML source from Wikipedia

    with open("temp.xml",'w') as t: #write HTML to xml format
        t.write(HTML)

    table_of_contents = []
    dict_of_section_info = {}

    #This extracts the info in the table of contents
    with open("temp.xml",'r') as r:
        for line in r:
            if "toclevel" in line: 
                new_string = line.partition("#")[2]
                content_title = new_string.partition("\"")[0]
                tbl = string.maketrans("_"," ")
                content_title = content_title.translate(tbl)
                table_of_contents.append(content_title)

    print wp.page(search).section("Aortic rupture") #this is None, but shouldn't be

    for item in table_of_contents:
        section = wp.page(search).section(item).encode("UTF-8")
        print section
        if section == "":
            continue
        else:
            dict_of_section_info[item] = section

    with open("Section_Info.txt",'a') as sect:
        sect.write(search)
        sect.write("------------------------------------------\n")
        for item in dict_of_section_info:
            sect.write(item)
            sect.write("\n\n")
            sect.write(dict_of_section_info[item])
        sect.write("####################################\n\n")

add_section_info("Abdominal aortic aneurysm")

我不明白的是，例如，如果我运行add_section_info("HIV")，它会完美运行。

导入的维基百科源代码为here

上面代码的输出是这样的：

Abdominal aortic aneurysm

Signs and symptoms
Traceback (most recent call last):
  File "/home/pharoslabsllc/Documents/wikitest.py", line 79, in <module>
add_section_info(line)
  File "/home/pharoslabsllc/Documents/wikitest.py", line 30, in add_section_info
    section = wp.page(search).section(item).encode("UTF-8")
AttributeError: 'NoneType' object has no attribute 'encode'

Answer 1

page 方法永远不会返回 None（您可以在源代码中轻松查看），但是如果找不到标题，section 方法确实返回None。见documentation：

section(section_title)

从self.sections 获取部分的纯文本内容。 如果没有找到section_title，则返回None，否则返回一个空白字符串。

所以答案是您所指的维基百科页面没有标题为Aortic rupture 的部分，就图书馆而言。

查看维基百科本身，Abdominal aortic aneurysm 页面似乎确实有这样的部分。

请注意，如果您尝试检查 wp.page(search).sections 的值，您会得到：[]。 IE。 库似乎没有正确解析这些部分。

---

从找到here的库的源代码可以看到这个测试：

section = u"== {} ==".format(section_title)
try:
  index = self.content.index(section) + len(section)
except ValueError:
  return None

但是：

In [14]: p.content.find('Aortic')
Out[14]: 3223

In [15]: p.content[3220:3220+50]
Out[15]: '== Aortic ruptureEdit ===\n\nThe signs and symptoms '
In [16]: p.section('Aortic ruptureEdit')
Out[16]: "The signs and symptoms of a ruptured AAA may includes severe pain in the lower back, flank, abdomen or groin. A mass that pulses with the heart beat may also be felt. The bleeding can leads to a hypovolemic shock with low blood pressure and a fast heart rate. This may lead to brief passing out.\nThe mortality of AAA rupture is up to 90%. 65–75% of patients die before they arrive at hospital and up to 90% die before they reach the operating room. The bleeding can be retroperitoneal or into the abdominal cavity. Rupture can also create a connection between the aorta and intestine or inferior vena cava. Flank ecchymosis (appearance of a bruise) is a sign of retroperitoneal bleeding, and is also called Grey Turner's sign.\nAortic aneurysm rupture may be mistaken for the pain of kidney stones, muscle related back pain."

注意Edit ==。换句话说，该库有一个错误，它没有考虑到要编辑的链接。

相同的代码适用于HIV 的页面，因为在该页面中，标题旁边没有edit 链接。我不知道为什么会这样，无论如何它看起来像是库的错误或缺点，所以你应该在它的问题跟踪器上打开一张票。

与此同时，您可以使用以下简单的修复方法：

def find_section(page, title):
    res = page.section(title)
    if res is None:
        res = page.section(title + 'Edit')
    return res

并使用此函数而不是使用.section 方法。但是，这只能是临时修复。

Answer 2

wp.page(search).section(item) 未找到您要查找的部分，并返回 None。您不检查它并尝试将值作为字符串处理；这预计会失败。