what does re.sub do in python code example

Example 1: re.sub in python example

import re

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

Example 2: re sub python

# From Grepper Docs
>>> re.sub('-{1,2}', dashrepl, 'pro----gram-files')
'pro--gram files'
>>> re.sub(r'\sAND\s', ' & ', 'Baked Beans And Spam', flags=re.IGNORECASE)
'Baked Beans & Spam'