Python爬蟲

Introduction

用途:

針對目標網站自動擷取資訊
將非表格的資料轉換成可結構化的資料
追蹤資料變更

例如:

社群:流行趨勢、熱門話題
股票:追蹤股票趨勢、資料分析
線上商店:取得價錢貨比三家
網路書店:指定主題的圖書清單

Python set up

Jupyter notebook

pip3 install jupyter

google colab

下載requests 和 beautiful soup套件

pip3 install --user --upgrade requests bs4

在命令提示字元打下:

瀏覽網頁的步驟

```
輸入URL網址
```

根據HTTP請求回應至瀏覽器(通常為HTML)

剖析網頁內容(DOM) Document Object Document

```
瀏覽器根據DOM產生內容
```

HTTP通訊協定?

瀏覽器

伺服器

請求

回應

HTTP通訊協定

主從架構(Client-Server Architecture):

Client

Server

HTTP請求

HTTP回應

```
客戶端要求連線伺服端
```
```
伺服端允許
```

客戶端送出HTTP請求(GET請求/POST表單送回)

```
伺服端以HTTP回應請求
```

一個網頁要送出幾個請求?

URL網址:

http和https:前者為HTTP通訊協定，後者為HTTP加密傳輸版本
網域名稱(會透過DNS轉換成IP位址)
通訊埠號(http為80、https為443)
資源路徑
參數
區塊ID

通訊協定://伺服器位址:埠號/資源路徑?參數#區塊ID

標準:

requests

pip install requests

開發環境安裝:

測試網站: http://httpbin.org/

get:

import requests
url="網址"
response=requests.get(url)

變數response取得網頁資料的回應

text	html標籤字串
contents	非文字類位元組資料(bytes)
encoding	html編碼 e.g. UTF-8 or big5等等
status_code	狀態碼請求成功:200/requests.codes.ok 請求失敗(不存在):4xx (404) 伺服器錯誤:5xx
header	取得header
url	取得現在的url

回應後做出指示:

import requests
url="https://www.csghs.tp.edu.tw/"
response=requests.get(url)
if response.status_code==200:
  print(response.encoding)
  print(response.text)
else:
  print("HTTP請求失敗")

參數:

get_params={
  "key":"value"      
}

url="目標網址"
response=requests.get(url,params=get_params)

import requests
url="http://httpbin.org/get"
params_get={"name":"Phoebe","year":"17"}
response=requests.get(url,params=params_get)
print(response.text)

import requests
url="https://www.csghs.tp.edu.tw/"
params_get={
  "s":"行事曆"
}
response=requests.get(url,params=params_get)
print(response.text)

post:

http://httpbin.org/post

參數:

post_data={
  "key":"value"
}
url="目標網址"
response=requests.post(url,data=post_data)

import requests
url="http://httpbin.org/post"
post_data={"name":"Phoebe","year":"17"}
response=requests.post(url,data=post_data)
print(response.text)

headers:

過量請求會導致網頁過載
避免被偵測為爬蟲
設定請求使用者代理

header={
  "User-Agent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/108.0.0.0 Safari/537.36"
}

瀏覽網頁時送出的請求，讓我們看起來不是爬蟲

(其實完整的長這樣)

header={
	"Accept": "application/json",
	"Accept-Encoding": "gzip, deflate",
	"Accept-Language": "zh-TW,zh;q=0.9,en-US;q=0.8,en;q=0.7",
	"Host": "httpbin.org",
	"Referer": "http://httpbin.org/",
	"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/108.0.0.0 Safari/537.36",
	"X-Amzn-Trace-Id": "Root=1-639b115a-5c22c80d7c1dc204593dbcd6"
}

url="目標網址"
response=requests.get(url,headers=header)

Beautiful soup

測試用小網站:

https://fchart.github.io/Elements.html

import requests
from bs4 import BeautifulSoup

url = "https://www.csghs.tp.edu.tw/"

response = requests.get(url)
soup = BeautifulSoup(response.text, "html.parser") 
#"lxml"較快 "html.parser"為預設
print(soup.prettify()) #排版

parasing

將HTML網頁建立成HTML標籤物件的階層結構，以便快速定位和取出所需要的標籤

tag
select_one(),select()
find(),find_all()

方法	說明
select_one()	參數CSS搜尋HTML標籤，回傳第一個符合的
select()	參數CSS搜尋HTML標籤，回傳所有符合的
find()	搜尋HTML標籤，回傳第一個符合的
find_all()	搜尋HTML標籤，回傳所有符合的

tag

import requests
from bs4 import BeautifulSoup

url = "https://www.csghs.tp.edu.tw/"

response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup("a")
for tag in tags:
  print(tag.get("href",None))

import requests
from bs4 import BeautifulSoup

url = "https://www.csghs.tp.edu.tw/"

response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
print(soup.title.text)

直接點

屬性or方法	說明
tag.text	取得html標籤內容
tag.attrs	取得標籤所有屬性的字典
tag.get("href",None)	取得第一個參數href，若沒有輸出None
tag.string	取得內容

import requests
from bs4 import BeautifulSoup

url = "https://www.csghs.tp.edu.tw/"

response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup("a")
tag=tags[12]
print("URL:",tag.get("href",None))
print("標籤內容:",tag.text)
print("屬性:",tag.attrs)

範例:

select_one()

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup.select_one("h2")
print("h2:",tags.text)

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup.select_one("#q2")
tag2=tags.select_one("b")
print("b:",tag2.text)

the 混

id屬性需在前面加上'#'

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup.select("b")
print("b0",tags[0].text)
print("b1",tags[1].text)
print("b2",tags[2].text)

select()

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup.select(".response")
print("li:",tags[0].text)
print("li:",tags[1].text)

class屬性可套用於多個標籤，因此需使用select一次讀取

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup.find("h2")
print("h2:",tags.text)

find()

find_all()

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup.find_all("b")
print("b0:",tags[0].text)

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup.find("li",{"id":"q2"})
tag_q=tags.find("b")
print("Q:",tag_q.text)
tag_a=tags.find_all("li",{"class":"response"})
for tag in tag_a:
  print("A:",tag.text)

class_()

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tags=soup.find("li",{"id":"q2"})
tag_q=tags.find("b")
print("Q:",tag_q.text)
tag_a=tags.find_all("li",class_="response")
for tag in tag_a:
  print("A:",tag.text)

limit()

import requests
from bs4 import BeautifulSoup

url = "https://fchart.github.io/Elements.html"
response = requests.get(url)
soup = BeautifulSoup(response.text, "lxml")
tag_a=soup.find_all("li",class_="response",limit=3)
for tag in tag_a:
  print("A:",tag.text)

爬蟲實作

以PTT為例

https://www.ptt.cc/bbs/index.html

去PTT挑一個自己喜歡的版面

import requests
url = 'https://www.ptt.cc/bbs/PokeMon/index.html'
response = requests.get(url)

抓起來

從標題下手->

til=soup.find_all("div",class_="title")

印出所有標題->

til[0],til[1],til[2]...
->使用迴圈取出

for t in til:
  if t.a!=None:
    print(t.a.text)

稍作改良

import requests
from bs4 import BeautifulSoup

url = 'https://www.ptt.cc/bbs/PokeMon/index.html'

response = requests.get(url)

soup = BeautifulSoup(response.text, "html.parser")
til=soup.select("div.title a")
for t in til:
  print(t.text)

Cookie處理

會遭到阻擋

_ga=GA1.2.854868822.1671121301; _gid=GA1.2.813480667.1671121301; over18=1

header={
  "cookie":"over18=1"
}

cookie={
  "over18":"1"
}

response = requests.post(url,headers=header)

response = requests.get(url,cookies=cookie)

import requests
from bs4 import BeautifulSoup
header={
  "cookie":"over18=1"
}

url = 'https://www.ptt.cc/bbs/Gossiping/index.html'

response = requests.post(url,headers=header)
soup=BeautifulSoup(response.text,"lxml")
til=soup.select("div.title a")
for t in til:
  print(t.text)

最終版本:

爬圖

import requests
from bs4 import BeautifulSoup

url = "目標網址"

response = requests.get(url)

soup = BeautifulSoup(response.text, 'html.parser')

起手

往上找id -> 為id=main-container中 div的img

photo=soup.select_one("#main-container img")

https://www.ptt.cc/bbs/Pet_Get/M.1631051441.A.6C7.html

獲取網址:

phurl = "https:" + photo.get("src")

import requests
from bs4 import BeautifulSoup

url = "https://www.ptt.cc/bbs/Pet_Get/M.1631051441.A.6C7.html"

response = requests.get(url)

soup = BeautifulSoup(response.text, 'html.parser')
photo=soup.select_one("#main-container img")
phurl = "https:" + photo.get("src")
print(phurl)

印出來確認:

創建資料夾:

import os
if not os.path.exists("Pet"): #創資料夾
  os.mkdir("Pet")

for chunk in response.iter_content(100000):
    FGOFile.write(chunk)
FGOFile.close #關閉資料夾

迭代圖片中的區塊:

100000/次

import requests
from bs4 import BeautifulSoup
import os

url = "https://www.ptt.cc/bbs/Pet_Get/M.1631051441.A.6C7.html"

response = requests.get(url)

if not os.path.exists("Pet"): #創資料夾
  os.mkdir("Pet")

soup = BeautifulSoup(response.text, 'html.parser')
photo=soup.select_one("img")
phurl = "https:" + photo.get("src")
print(phurl)
PetFile = open(os.path.join('Pet', os.path.basename(phurl)), 'wb')
for chunk in response.iter_content(100000):
    PetFile.write(chunk)
PetFile.close

爬所有的圖:

import requests                                                          
import os                                                                  
import bs4                                                           

url="https://www.ptt.cc/bbs/Pet_Get/M.1631051441.A.6C7.html"         
request = requests.get(url)                                        
data = bs4.BeautifulSoup(request.text, "html.parser")                
imageData = data.find_all('img')      
path=r"C:\Users\Phoebe Wu\Pet"                                   
if (os.path.exists(path) == False):                                  
  os.makedirs(path)                                                 
imgList = []                                                          
lenth = len(imageData)                                                
for x in range(lenth):                                                  
   imgList.insert(x,imageData[x].attrs["src"])                         
for i in range(lenth):                                                
   getImage = requests.get(imgList[i])                                
   image = getImage.content                                           
   imageSave = open(path+"\img"+str(i)+".jpg","wb")                    
   imageSave.write(image)                                             
   imageSave.close()                                                  
   print("img"+str(i)+".jpg"+"下載成功")
print("下載完成")

Sources:

https://www.learncodewithmike.com/2020/09/7-tips-to-avoid-getting-blocked-while-scraping.html

PythonWebScratch

By Wu Phoebe

Python爬蟲

瀏覽網頁的步驟

PythonWebScratch

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