How to remove all characters except letters and numbers in Python? (code example)

String manipulation is a very important task in daily coding and web development; for example: most requests and responses in HTTP queries are in the form of strings, and sometimes we need to delete some useless data. The following article will introduce you to some Python methods to delete all characters except letters and numbers in a specified string. I hope it will be helpful to you.

Method 1: Use the re.sub() function

Regular expression in Python The function is very powerful, and the re.sub() function is a regular replacement string in Python. The re.sub() function can use regular expressions to match the string to be replaced, and then replace the matched string with another string.

Syntax:

re.sub(pattern , repl , string , count = 0 , flags = 0)

"sub" in this function represents substring (SubString), search in the given string (3rd parameter) A specific regular expression pattern (1st argument) that, when found, is replaced with the replacement substring pattern in repl (2nd argument), counting the number of times this occurs, checking and keeping.

Code example:

import re 
  
# 初始化字符串
ini_string = "123ab#cg|+f&ph*&^p:, .@! eiw"
  
#输出初始字符串
print ("初始字符串 : ", ini_string) 
  
# 使用re.sub()函数
result = re.sub('[\W_]+', '', ini_string) 
  
# 输出替换后的字符串
print ("替换后的字符串：", result)

Output:

初始字符串 :  123ab#cg|+f&ph*&^p:, .@! eiw
替换后的字符串： 123abcgfphpeiw

Method 2: Use isalpha() isnumeric() join() Method

The isalpha() method is a built-in method of Python for string processing, which can check whether the string consists only of letters. Returns "True" if all characters in the string are letters, "False" otherwise.

The isnumeric() method is a built-in method of Python for string processing, which can check whether the string consists only of numbers. Returns "True" if all characters in the string are numeric characters, "False" otherwise.

The join() method is used to join elements in the sequence with specified characters to generate a new string.

Code example:

import re 
  
# 初始化字符串
ini_string = "123ab#cg|+f&ph*&^p:, .@! eiw"
  
#输出初始字符串
print ("初始字符串 : ", ini_string) 
  
# 使用isalpha()+isnumeric()+join()方法
getVals = list([val for val in ini_string 
               if val.isalpha() or val.isnumeric()]) 
  
result = "".join(getVals) 
  
# 输出替换后的字符串
print ("替换后的字符串：", result)

Output:

初始字符串 :  123ab#cg|+f&ph*&^p:, .@! eiw
替换后的字符串： 123abcgfphpeiw

Method 3: Use isalnum() join()

isalnum() function is used to check whether all characters in a given string are letters or numbers.

Code example:

import re 
  
# 初始化字符串
ini_string = "123ab#cg|+f&ph*&^p:, .@! eiw"
  
#输出初始字符串
print ("初始字符串 : ", ini_string) 
  
# 使用isalnum()+join()方法
getVals = list([val for val in ini_string if val.isalnum()]) 
result = "".join(getVals) 
  
# 输出替换后的字符串
print ("替换后的字符串：", result)

Output:

初始字符串 :  123ab#cg|+f&ph*&^p:, .@! eiw
替换后的字符串： 123abcgfphpeiw

Related video tutorial recommendation: "Python Tutorial"

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