Notes on Python regular expressions

Article Directory

• 0, Preface
• 1, Regular expression pattern
• 2. Regular expression modifier - optional flag
• • 2.1, `re.IGNORECASE`(`re.I`)
  • 2.2, `re.ASCII` (`re.A`)
  • 2.3, `re.DOTALL` (`re.S`)
  • 2.4, `re.MULTILINE`(`re.M`)
  • 2.5, `re.VERBOSE`(re.X)
  • 2.6, Superposition of modifiers
• 3, Regular expression function
• • 3.1. Function to find a single match
  • • Example 3.1.1
    • Example 3.1.2
    • Example 3.1. 3
  • 3.2. Function to find multiple matches
  • • Example 3.2.1
  • 3.3. Split
  • • Example 3.3.1
##

import re

0、Foreword

This note is based on the novice tutorial and the Zhihu tutorial, and incorporates some of my own learning experiences.

1. Regular expression pattern

The highlights are my additions, because they can indeed be matched according to the actual situation.

I was a bit lazy here and took a screenshot of the novice tutorial.

2. Regular expression modifier - optional flag

2.1.re.IGNORECASE(re.I )

Although section 1 is a constant, we must briefly mention the

re.findall function because it is the function throughout this section.
re.findall(pattern, string, flag=0): Search from any position in the string and return a list. pattern is the character (string) to be matched, string is the search source, flag is the modifier, the default is 0

The function of re.I is to ignore the case of characters

text = "I'm Jasmine-Feng. My student number is No. 321432"pattern = r"Jasmine-FENG"print('Default: ', re.findall(pattern,text))print('Ignore upper/lower case: ', re.findall(pattern,text,flags=re.I))

N.B. The pattern is assigned a r string . The function of this r string is to avoid Escape, r is the abbreviation of raw, which means keeping it as is. See this blog post. Generally speaking, this r string will be used when using regular expressions.

Default:  []Ignore upper/lower case:  ['Jasmine-Feng']Process finished with exit code 0

By default, it is case-sensitive and ENG cannot be found; if it is not distinguished, eng can be found.

2.2. The function of re.ASCII(re.A)

##re.A

is Only matches characters supported by ASCII code, so which characters specifically do you mean? The picture below is from Baidu Encyclopedia.
Chinese characters are not included in this, so if the modifier is re.A
, then the Chinese characters cannot be matched~<pre class="brush:php;toolbar:false">text = &quot;我是Jasmine-Feng. 我的学号是No. 321432&quot;pattern = r&quot;\w+&quot;print('Default: ', re.findall(pattern,text))print('ASCII: ', re.findall(pattern,text,flags=re.A))</pre>

\w

is used to match one or more alphanumeric and underlined Chinese characters <pre class="brush:php;toolbar:false">Default:  ['我是Jasmine', 'Feng', '我的学号是No', '321432']ASCII:  ['Jasmine', 'Feng', 'No', '321432']Process finished with exit code 0</pre>

2.3,

re.DOTALL（re.S）In the regular expression pattern,

.

is used

text = "我\t是Jasmine-F\neng. 我%的◉学号是No. 321432"pattern = r'.*'print('Default: ', re.findall(pattern,text))print('DOTALL: ', re.findall(pattern,text,re.S))

.*

is used to match characters with a length of at least 0 (String), emmm, it seems like nonsense? In fact, as long as the entire paragraph is not truncated by a newline character, you can get the entire string (plus an empty string). <pre class="brush:php;toolbar:false">Default:  ['我\t是Jasmine-F', '', 'eng. 我%的◉学号是No. 321432', '']DOTALL:  ['我\t是Jasmine-F\neng. 我%的◉学号是No. 321432', '']Process finished with exit code 0</pre>

2.4、

re.MULTILINE(re.M)

$

Matching positioning To the end of the string, ^ locates the beginning of the string. By default, if you wrap a new line, you cannot locate the beginning/end of the new line. However, modifying it with re.M will Yes, that is multi-line mode. <pre class="brush:php;toolbar:false">text = &quot;我\t是Jasmine-F\neng. 我%的◉\n学号是No. 321432&quot;pattern = r'.$'pattern2 = r'^.'print('Default, end: ', re.findall(pattern, text))print('MULTILINE, end: ', re.findall(pattern, text, re.M))print('Default, start: ', re.findall(pattern2, text))print('MULTILINE, start: ', re.findall(pattern2, text, re.M))</pre> <pre class="brush:php;toolbar:false">Default, end:  ['2']MULTILINE, end:  ['F', '◉', '2']Default, start:  ['我']MULTILINE, start:  ['我', 'e', '学']Process finished with exit code 0</pre>

2.5、

re.VERBOSE(re.X)verbose means "detailed and lengthy", through this modifier Comments can be added to

regular expression

. Note that you are adding it to pattern, not to text! At first I thought I could add comments to text, but I couldn’t get the result after debugging for a long time. . . <pre class="brush:php;toolbar:false">text = '朋友们好啊！我是xxxxxx拳掌门人xxx~'pattern = r'''朋友们  # 主语               好啊！  # 谓语            '''print(re.findall(pattern, text,re.VERBOSE))</pre> <pre class="brush:php;toolbar:false">['朋友们好啊！']Process finished with exit code 0</pre>

2.6. Superposition of modifiers

Use

|

to superimpose modifications. <pre class="brush:php;toolbar:false">text = 'Hello everybody!\n我是xxxxxx拳掌门人xxx~'pattern = r'BODY.*$'print(re.findall(pattern, text, re.I))print(re.findall(pattern, text, re.M))print(re.findall(pattern, text, re.M | re.I))</pre> <pre class="brush:php;toolbar:false">[][]['body!']Process finished with exit code 0</pre>

3. Regular expression function

3.1. Function to find a single match

Function##searchmatch##fullmatchIn fact, I originally wrote my own example, but the browser closed it for me by mistake and did not save it. (My mentality exploded directly

Function
Start search from any position
Search from the beginning, no need to match exactly
Search from the beginning, it must match exactly

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