Using regex to remove comments from source files

re.sub returns a string, so changing your code to the following will give results:

def removeComments(string):
    string = re.sub(re.compile("/\*.*?\*/",re.DOTALL ) ,"" ,string) # remove all occurrences streamed comments (/*COMMENT */) from string
    string = re.sub(re.compile("//.*?\n" ) ,"" ,string) # remove all occurrence single-line comments (//COMMENT\n ) from string
    return string

What about "//comment-like strings inside quotes"?

OP is asking how to do do it using regular expressions; so:

def remove_comments(string):
    pattern = r"(\".*?\"|\'.*?\')|(/\*.*?\*/|//[^\r\n]*$)"
    # first group captures quoted strings (double or single)
    # second group captures comments (//single-line or /* multi-line */)
    regex = re.compile(pattern, re.MULTILINE|re.DOTALL)
    def _replacer(match):
        # if the 2nd group (capturing comments) is not None,
        # it means we have captured a non-quoted (real) comment string.
        if match.group(2) is not None:
            return "" # so we will return empty to remove the comment
        else: # otherwise, we will return the 1st group
            return match.group(1) # captured quoted-string
    return regex.sub(_replacer, string)

This WILL remove:

• /* multi-line comments */
• // single-line comments

Will NOT remove:

• String var1 = "this is /* not a comment. */";
• char *var2 = "this is // not a comment, either.";
• url = 'http://not.comment.com';

Note: This will also work for Javascript source.