Python re.sub multiline on string

Question

I try to use the flag re.MULTILINE.

I read these posts : Bug in Python Regex? (re.sub with re.MULTILINE), Python re.sub MULTILINE caret match but i

Answer 1

You need to replace re.MULTILINE with re.DOTALL/re.S and move out period outside the character class as inside it, the dot matches a literal ..

Note that re.MULTILINE only redefines the behavior of ^ and $ that are forced to match at the start/end of a line rather than the whole string. The re.DOTALL flag redefines the behavior of . inside the pattern outside the character class only. It starts matching a newline symbol, too.

So, the regex you could use for the current example: /\*.*?\*/. It matches a literal /* with /\*, then .*? matches as few any symbols as possible up to and including */ (matched with \*/).

See the code demo:

txt = """\n\
<?php\n\
/* Multi-line\n\
comment */\n\
$var = 1;\n"""
new_txt = re.sub(r'/\*.*?\*/', '', txt, flags=re.S)
print("\n=========== TXT ============")
print(txt)
print("\n=========== NEW TXT ============")
print(new_txt)

See IDEONE demo

However, it is not the best solution, as in most cases multiline comments are very long. The best is an unrolling-the-loop technique. The regex above can be "unrolled" like this:

/\*[^*]*(?:\*(?!/)[^*]*)*\*/

See the regex demo