mystr = r'''documentclass[12pt]{article}
usepackage{amsmath}
title{LaTeX}
begin{document}
section{Introduction}
This is introduction paragraph
section{Non-Introduction}
This is non-introduction paragraph
section{Sample section}
This is sample section paragraph
end{document}'''

['This is introduction paragraph','This is non-introduction paragraph','    This is sample section paragraph']

my_string = "a quick brown fox jumps over a lazy dog than a quick elephant"
word = "a "
my_string.split(word)

['', 'quick brown fox jumps over ', 'lazy dog than ', 'quick elephant']

import re
str_ = "a quick brown fox jumps over a lazy dog than a quick elephant"


print(re.split(r's?babs?',str_))

# ['', 'quick brown fox jumps over', 'lazy dog than', 'quick elephant']