how to write this re?

[Mindy]

Hey, I want to find strings which includes "string1"
but not includes "string2" in a bunch of strings
called "lines", how can I write this regular
expression in Python?
For "axystring1bdestring2lkj",
"aaastring1bbbccc","aaabbbstring2poi","aaabbbcccddd" I
only want to get the string "aaastring1bbbccc" but my
program got two strings: "axystring1bdestring2lkj" and
"aaastring1bbbccc". So in my regular expression,
(?!string2) didn't work at all. I know I shouldn't
write this,but I really don't know how to express "not
including string2".

My regular expression is like:
r=re.search(r'(.*)string1(.*)(?!string2)(.*)',lines)
if r:
	string1 = r.string

Thanks for any hints!


=====
Cheers
-Mindy

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