python - Convert an integer to its negative -

i'm trying write code if occurence happens, specific number has change -that number. have following code far:

x=6  words in foo:    if "bar" in words:       crazy_function(x)    else:       pass 

if word "bar" in words, x need come out -6, if not in words, needs come out +6. in cases x=-6 in case needs become positive if bar in words. need replace "crazy_function()" works.

use negation operator:

x=6  words in foo:   if "bar" in words:     x = -x;