What does “sub” mean in Python?

In Python, the sub function is a part of the re library that is used for regular expression string replacement. The purpose of sub is to replace strings that match a specific regular expression with a specified string.

The specific syntax is: re.sub(pattern, repl, string, count=0, flags=0)

1. Regular expression pattern is used to match the strings that need to be replaced.
2. repl: the string to be replaced.
3. string: the string in which replacement operation will be performed.
4. Count: an optional parameter that specifies the number of replacements to perform. The default value is 0, indicating that all matching strings will be replaced.
5. Flags: an optional parameter used to specify the matching mode for the regular expression.

The sub function can identify specific patterns in a string using regular expressions, and replace them with a specified string. This is commonly used in string and text processing for tasks such as replacing certain characters or substrings, removing illegal characters, formatting text, and more.