5 minutes to learn regular expressions

The role of regular expressions ：

Use one pattern String to match a similar segment in the target string . To put it bluntly , One day you see a string , You want to pull a piece out of it , You use regular expressions to match the paragraph you want

Write regular steps

1. First, fix the structure . Fixed things are written directly , Use parentheses instead of fixed or variable .
Case study 1：
For example, there is a kind of string
“admin-api-8xd5sdfa9p-asdf4”
“admin-api-qos3difd1c-2q5gh”
How to match such strings ？
First, fix the structure ：”admin-api-()-()” , That's it . Keep writing directly , Use parentheses instead of parentheses , This is the structure .
Case study 2：
For example, find out from the string 11 Bit of mobile phone number
The target string is ：” full name ： Zhang Wei ; Telephone ：[phone]”
We just want to match the phone number , Others don't . Phone number 11 Bits are not fixed .
Then the structure is a pair of parentheses “()” , That's it .

2. Find the regular characters you need in the quick look-up table below and fill them in the structure
Regular characters fall into two categories , One is content , A class that represents the number of occurrences .
such as . Belongs to the content character ,* The number character , that .* It means any string with any content and length . This is the most commonly used .
such as [0-9] Express 0-9 One of the numbers in , Is a content character ,{11} Appear 11 Time ,{10,20} Appear 10 Time to 20 Time , These are the number characters . therefore [0-9]{11} You can match the continuity 11 Digit number , That is, the telephone number .
So the complete regular expression of the above two cases is like this ：
“admin-api-(\w{10})-(\w{5})”
“(\d{11})” perhaps “([0-9]{11})”

3.（ the selected readings ）Python General code for matching strings using regular expressions

import re  # re yes python Function modules of the standard library , amount to java Medium Maven package 
pattern = re.compile(“admin-api-(\w{
    10})-(\w{
    5})”)  #  Compile your regular expression , Fast execution 
groups = pattern.match(“ Target string , such as admin-api-8xd5sdfa9p-asdf4”)
# groups It's a list , The first element is the longest string matched , Then the following elements are the matching contents of the first parenthesis 、 What the second parenthesis matches ……
# match The function is an ab initio match , If the string you want to match is not at the beginning of the target string , Then use groups = pattern.findall() 
print(groups[0]) #  Print the longest complete string you can match , This is supposed to be  admin-api-8xd5sdfa9p-asdf4
print(groups[1]) #  The string to which the first parenthesis matches , This is supposed to be  8xd5sdfa9p

Regular quick look-up table

In the structure () Represent the changing part , The following table also shows (?: ) (?=) (?!) Usage of .