How is the re library in Python used?

The re library is one of the standard libraries in Python that is used for regular expression operations, including pattern matching, searching, and replacing strings.

To use the re library, you first need to import it.

import re

Next, the functions in the re library can be used to perform various regular expression operations.

1. The re.match() function tries to match a pattern from the beginning of a string. If it successfully finds a match, it returns a match object; otherwise, it returns None.

match_obj = re.match(pattern, string)

1. re.search() scans the entire string and returns the first successfully matched object.

search_obj = re.search(pattern, string)

1. re.findall(): Returns a list containing all non-overlapping matches of the pattern in a string.

match_list = re.findall(pattern, string)

1. re.finditer() returns an iterator containing all non-overlapping matches of the pattern in the string.

match_iter = re.finditer(pattern, string)

1. re.sub() is used to replace parts of a string that match a certain pattern.

new_string = re.sub(pattern, replacement, string)

The above are just some common functions in the re library, where pattern represents the regular expression pattern, string represents the string to be matched, and replacement represents the string to replace.

When using regular expressions, commonly used meta-characters can be employed, such as “.” which represents matching any character, “^” indicating matching the start of a string, and “$” indicating matching the end of a string.

For more detailed usage, refer to the official documentation of the re library at https://docs.python.org/3/library/re.html.