How to use regular expressions in Python?

Python is a powerful programming language that supports the use of regular expressions for text manipulation. As data analysis and text processing become more and more common in all walks of life, mastering the skills of regular expressions has become an increasingly important basic skill. In this article, we will learn how to use regular expressions in Python.

1. Import the re module

Using regular expressions in Python requires importing the re module. Of course, before using regular expressions, we need to first be familiar with the syntax rules of regular expressions. Here are some basic regular expression symbols and their meanings:

##W Matches other characters except letters, numbers, underscores or Chinese characters s Matches any white space characters, including spaces, tabs, and newlines Characters, etc.Smatches any non-whitespace characters^matches the beginning of the string $Match the end of the string*Match 0 or more timesMatch 1 or more times?Match 0 or 1 times{n}Match exactly n times{n,}Match n times or more Multiple times{m,n}Match m~n times[...] Matches any characters in square brackets, including character ranges, excluded characters, etc. (...)Capture matching substrings(?:…)Does not capture matching substrings(?=...) Positive positive pre-check(?!...)Positive negative pre-check(?< ;=...)Reverse positive pre-check(?Reverse negative pre-check

Symbol	Meaning
.	Matches any character, except newline characters
d	Matches digits
D	matches non-digits
w	matches letters, numbers, underscores or Chinese characters

Matching strings
2. Let’s try to use the re module for simple string matching. For example, we want to match substrings in the form of "hello world" in the string. The code is as follows:
   

import re

# 声明一个字符串
str1 = "hello world"

# 定义正则表达式
pattern = "hello world"

# 使用 re 模块进行匹配
result = re.search(pattern, str1)
print(result.group())

Output result:

hello world

Special characters

When we need to search for some special characters, we need to add escape characters () in the regular expression. For example:

Search for words ending with parentheses:

• # 定义正则表达式
  pattern = r"w+($"
  
  # 使用 re 模块进行匹配
  result = re.search(pattern, "I have a list (item1, item2).")
  print(result.group())

Output results:

list(

Search for URLs containing .:

• # 定义正则表达式
  pattern = r"https?://S+.w+(?<!/)$"
  
  # 使用 re 模块进行匹配
  result = re.search(pattern, "Here is a link: https://www.google.com.")
  print(result.group())

Output result:

https://www.google.com

Match multiple substrings
4. Sometimes, we need to match multiple substrings in the text. In this case we can use findall function. For example, if we want to find all email addresses in a string, the code looks like this:
   

# 定义正则表达式
pattern = r"w+@w+.w{2,3}"

# 使用 re 模块进行匹配
result = re.findall(pattern, "Please contact me at alice@gmail.com or bob@hotmail.com")
print(result)

Output result:

['alice@gmail.com', 'bob@hotmail.com']

Replace the string
5. We You can also use regular expressions to replace strings in Python. For example, to replace all numbers in a string with * signs, the code is as follows:
   

# 定义正则表达式
pattern = r"d"

# 使用 re 模块进行匹配和替换
result = re.sub(pattern, "*", "12345678")
print(result)

Output result:

********

Summary
6. In this article , we learned the basics of using regular expressions in Python. Remember that regular expressions can make many tasks in text processing easier. Mastering the basics of regular expressions is an essential skill for data scientists, machine learning engineers, and software developers.
   

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