Scraping 2 How to scrape
Aidemy 2020/9/30
Introduction
Hello, it is Yope! I am a liberal arts student, but I was interested in the possibilities of AI, so I went to the AI-specialized school "Aidemy" to study. I would like to share the knowledge gained here with you, and I am summarizing it on Qiita. I am very happy that many people have read the previous summary article. Thank you!
This is the second post of scraping. Nice to meet you.
- This article is a summary of what you learned in "Aidemy" "in your own words". It may contain mistakes and misunderstandings. Please note.
What to learn this time
・ Scraping method (Refer to scraping 1 for preparatory crawling)
・ Scraping multiple pages
Scraping
How to scrape
・ (Review) Scraping is to acquire a Web page and extract necessary data from it.
-There are two types of scraping methods, "regular expression (re module)" or "use a third-party library", but this time the major method is __ "use a third-party library". "Scraping is done by the __ method.
About HTML and XML
-XML is a __markup language __ that directly builds the same Web pages as HTML. It is more extensible than HTML.
-In HTML and XML, there is text surrounded by something like ** \
<\ title> **, of which the whole is called <strong>element</strong> and <title> is __. Say tag __.
-There is also a notation such as \ <html lang = "ja">, which means that the <strong>lang attribute is ja</strong>, that is, the language is Japanese.
-In the "Beautiful Soup" library used for scraping this time, the title etc. is acquired from this element name.</p>
<h2>Scraping with Beautiful Soup (preparation for analysis)</h2>
<p>-You can easily scrape by using the <strong>BeautifulSoup (decoded web page, "parser") __ method.
-</strong> Parser __ is a program that analyzes (parses) character strings, and there are several types for each feature, and one of them is specified. Examples include "html.parser" which does not require an additional library, "lxml" which can process at high speed, and "xml" which corresponds to XML.</p>
<pre><code class="language-python">#Import requests to crawl and Beautiful Soup to scrape
from bs4 import BeautifulSoup
import requests
#Get url
url=requests.get("https://www.google.co.jp")
#Scraping (decoding is the url of the request module.The parser is done with text"xml"Specified as)
soup=BeautifulSoup(url.text,"xml")
</code></pre>
<h2>Scraping with BeautifulSoup (extracting necessary data)</h2>
<p>-Necessary data can be extracted from the parsed data performed in the previous section. There are the following two methods.
-If you put the parsed data in the variable soup, __soup.find ("tag name or attribute name") __ will extract only the first element with that tag or attribute. Also, if the find part is <strong>find_all</strong>, all the specified elements will be listed and extracted.
-If you want to scrape from the class attribute, add _<em>class</em>=" class attribute name" __ to the argument.</p>
<p>-If you put the parsed data in the variable soup, __soup.selected_one ("CSS selector") __ will extract only the first element that satisfies this. Also, if the selected_one part is <strong>select</strong>, all the specified elements will be listed and extracted.
-The __CSS selector is a method of showing elements in CSS representation. __ You can also use this to specify an element inside an element (ex) The h1 element inside a body element is "body> h1").</p>
<p>-Also, as a trick, you can copy elements and CSS selectors with Chrome's developer tools. Therefore, it is possible to extract the desired data in a visually easy-to-understand manner without having to bother to output the decoded data.</p>
<pre><code class="language-python">Google_title = soup.find("title") #<title>Google</title>
Google_h1 = soup.select("body > h1") #[](Empty list is output because there is no h1 element of body element)
</code></pre>
<p>-If the above is left as it is, Google_title will be output with the title tag attached, but by using <strong>text</strong>, only the text of these can be obtained.</p>
<pre><code class="language-python">print(Google_title.text) #Google
</code></pre>
<h2>Scraping multiple pages</h2>
<p>・ With the method so far, you can scrape only one page at a time. If you want to scrape multiple pages, you can get the URL of the other page from the link to the other page on the top page etc. __ and scrape all the URLs by iterative processing.
-The URL of other pages can be obtained by __the URL of the top page + the href attribute (link of each page) __ of the <a> element.</p>
<pre><code class="language-python">top="http://scraping.aidemy.net"
r=requests.get(top)
soup=BeautifulSoup(r.text,"lxml")
url_lists=[]
#Get the URL of another page from the link
#(The method is to first get all the a tags, use get to code the href attribute for each, and connect it to the topURL to make it a URL.)
urls = soup.find_all("a")
for url in urls:
url = top + url.get("href")
url_lists.append(url)
</code></pre>
<p>・ If you can get the URL of another page, actually scrape it. As mentioned above, scraping should be performed for all URLs by iterative processing.
-In the following, the titles of the photos (listed in the h3 tag) will be scraped from all the pages acquired in the previous section, and all will be acquired and displayed as a list.</p>
<pre><code class="language-python">photo_lists=[]
#Encode the page obtained in the previous section and then scrape the photo title with Beautiful Soup.
for url in url_lists:
r2=requests.get(url)
soup=BeautifulSoup(r2.text,"lxml")
photos=soup.find_all("h3")
#Add the title of the photo obtained by scraping to the list without the h3 tag.
for photo in photos:
photo_text=photo.text
photo_lists.append(photo_text)
print(photo_lists) #['Minim incididunt pariatur', 'Voluptate',...(Abbreviation)]
</code></pre>
<h1>Summary</h1>
<p>-When scraping a crawled page, first parse it with the <strong>BeautifulSoup</strong> method.
-Any data can be extracted from the parsed data. Use __find () __ or __selected_one () __ to extract.
-If you add <strong>text</strong> to the extracted data, tags etc. will be omitted and only the elements can be extracted.
-When scraping multiple pages at once, you can scrape them individually because you can scrape them by extracting the link from the __top page and connecting it to the base URL.</p>
<p>This time is over. Thank you for reading this far.</p>
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