分享興趣，傳播快樂，增長見聞，留下美好！
親愛的您，這裡是LearningYard學苑。今天小編為大家帶來“學習知多少（python篇）：正規表達式”，歡迎您的通路。
Share interests, spread happiness, increase knowledge, and leave a good legacy!
Dear you, this is The LearningYard Academy. Today Xiaobian brings you "Learn how much to know (python):regular expression”, welcome your visit.
一、概念
1, the concept
正規表達式是字元串處理的有力工具。它使用預定義的模式去比對一類具有共同特征的字元串，可以快速、準确完成複雜的查找、替換等處理要求。
Regular expressions are powerful tools for string processing. It uses predefined patterns to match a class of strings with common characteristics, and can quickly and accurately complete complex search, replace and other processing requirements.
正規表達式由元字元及其不同組合構成，通過構造正規表達式可以巧妙地比對任意字元串。
Regular expressions are made up of metacharacters and their different combinations, and regular expressions can be constructed to cleverly match arbitrary strings.
\s 比對空白字元
\w 比對任意字母/數字/下劃線
\W 和小寫 w 相反，比對任意字母/數字/下劃線以外的字元
\d 比對十進制數字
\D 比對除了十進制數以外的值
[0-9] 比對一個0-9之間的數字
[a-z] 比對小寫英文字母
[A-Z] 比對大寫英文字母
s matches whitespace characters
w matches any letters/numbers/underscores
W and lowercase w instead, match characters other than any letters/numbers/underscores
d matches decimal digits
D matches a value other than a decimal number
[0-9] matches a number between 0-9
[a-z] matches lowercase English letters
[A-Z] matches uppercase English letters
二、常用寫法
2. Common writing methods
正規表達式博大精深、變幻無窮，一下子全部記住是很難的，下面小編為大家總結了一些正常用法，大家可以記住然後在實際應用中不斷深入。
Regular expressions are broad and profound, endlessly changeable, it is difficult to remember them all at once, the following small series summarizes some conventional usage for you, you can remember and then continue to deepen in practical applications.
（1）最簡單的正規表達式是普通字元串，隻能比對自身。
（2）'[pjc]ython'可以比對'python'、'jython'、 'cython'。
（3）'[a-zA-Z0-9]'可以比對一個任意大小寫字母或數字。
（4）'[^abc]'可以比對一個任意除'a'、'b'、'c' 之外的字元。
（5）'python|perl' 可以比對 'python' 或 'perl'。
(6)r'(http://)?(www\.)?python\.org'隻能比對 'http://www.python.org'、'http://python.org'、'www.python.org'和'python.org'。
（7）'^http'隻能比對所有以 'http'開頭的字元串。
（8）(pattern)*：允許模式重複0次或多次。
（9）(pattern)+：允許模式重複一次或多次。
（10）(pattern){m,n}：允許模式重複m~n次，注意逗号後面不要有空格。
(1) The simplest regular expression is an ordinary string that can only match itself.
(2) '[PJC]YTHON' can match 'Python', 'JYTHON', 'Cython'.
(3) '[a-zA-Z0-9]' can match a letter or number of any case.
(4) '[^abc]' can match any character other than 'a', 'b', 'c'.
(5) 'python|perl' can match 'python' or 'perl'.
(6)r'(http://)? (www.)? 'python.org' can only match
'http://www.python.org', 'http://python.org', 'www.python.org', and 'python.org'.
(7) '^http' can only match all strings that start with 'http'.
(8) (pattern)*: Allows the pattern to repeat 0 or more times.
(9) (pattern)+: Allows the pattern to repeat one or more times.
(10)(pattern){m,n}: Allow the pattern to repeat m~n times, pay attention to no spaces after the comma.
三、案例
3. Cases
1、查找第一個比對串
2、查找所有1
3、\d比對數字[0-9]
4、?表示前一個字元比對0或1次
5、^比對字元串的開頭
6、re.I 忽略大小寫
7、使用正則提取單詞
8、隻捕獲單詞，去掉空格
9、補充上第一個單詞
10、使用split函數直接分割單詞
11、提取以m或t開頭的單詞，忽略大小寫
12、使用^查找字元串開頭的單詞
13、先分割，再查找滿足要求的單詞
14、貪心比對
15、非貪心比對
16、含有多種分割符
17、替換比對的子串
18、爬取百度首頁标題
1. Find the first matching string
2. Find all 1s
3, d matching number [0-9]
4、? Indicates that the previous character matched 0 or 1 times
5. ^ matches the beginning of the string
6、re. I Ignore case
7. Use regular extraction of words
8. Only capture words, remove spaces
9. Supplement the first word
10. Use the split function to directly split words
11. Extract words starting with m or t, ignoring case
12. Use ^ to find words at the beginning of a string
13. Divide first, and then find words that meet the requirements
14. Greedy matching
15. Non-greedy matching
16. Contains a variety of separators
17. Replace the matching substring
18. Crawl the title of Baidu's homepage
今天的分享就到這裡了。
如果您對今天的文章有獨特的想法,
歡迎給我們留言，
讓我們相約明天。
祝您今天過得開心快樂！
That's all for today's sharing.
If you have a unique idea for today’s article,
please leave us a message,
and let us meet tomorrow.
I wish you a happy day !
本文由learningyard新學苑原創，如有侵權，請聯系我們！
翻譯來源于谷歌翻譯
部分來源于
百度文庫
清華大學出版 董付國《Python程式設計基礎》
編輯&排版|百味
稽核|闫慶紅