Python教程：常用网页字符串处理技巧

首先一些Python字符串处理的简易常用的用法。其他的以后用到再补充。

1.去掉重复空格

s = "hello   hello   hello"
s = " ".join(s.split())

2.去掉所有回车（或其他字符或字符串）

s = "hello
hello
hello hello
"
print(s)
s = s.replace("
","")
print(s)

3.查找字符串首次出现的位置（没有返回-1）

s = "hello
hello
hello hello
"
print(s.find("
"))
print(s.find("la"))

4.查找字符串从后往前找首次出现的位置（没有返回-1）

s = "hello
hello
hello hello
"
print(s.rfind("
"))
print(s.rfind("la"))

5.将字符串转化成列表list

s = "hello
hello
hello hello
"
print(list(s))

6.查找所有匹配的子串

import re

s = "hello
hello
hello hello
"
print(re.findall("hello",s)) # hello也可以换成正则表达式

然后是网页字符串处理的高端用法：（综合运用requests模块，beautifulsoup模块，re模块等）

1.requests获取一个链接的内容并原封不动写入文件

import requests

r = requests.get("https://baike.baidu.com")
with open("test.html", "wb") as fd:
    for chunk in r.iter_content(100):
        fd.write(chunk)

2.读取一个文件的所有内容存到一个字符串里

# encoding : utf-8

with open("test.html","r",encoding="utf-8") as f:
    content = f.readlines()
content = "".join(content)
# content = content.replace("
","") # 如果想去掉回车可以加上这行
print(content)

3.把网页字符串用BeautifulSoup存起来处理

from bs4 import BeautifulSoup

soup = BeautifulSoup(content,"html.parser")
print(soup.prettify())

4.存到BeautifulSoup里之后这个字符串就可以任你摆布了，比如：提取出所有标签

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soup = BeautifulSoup(content,"html.parser")
print(soup.find_all("a"))

或者提取出所有标签和标签

soup = BeautifulSoup(content,"html.parser")
print(soup.find_all(["a","b"]))

import re
re.split("; |, ",str)

>>> a="Beautiful, is; better*than
ugly"
>>> import re
>>> re.split("; |, |*|
",a)
["Beautiful", "is", "better", "than", "ugly"]