From https://docs.python.org/2/library/re.html#regular-expression-syntax :
(?!...) Matches if ... doesn’t match next. This is a ne
Isaac(?!.*Asimov)
Use a negative lookahead for any sequence of characters ending in Asimov. [\s\S] or the DOTALL flag may be appropriate if you want to include newlines in the ..
[\s\S]
DOTALL
.