Python中用于查找以句点分隔的子字符串的正则表达式是什么？
例如：
Case 1: "something blah.foo another" return "blah.foo"
Case 2: "something blah.foo.what.not another" return "blah.foo.what.not"
Case 3: "something (blah.foo.what.not.aha) another" return "blah.foo.what.not.aha"
等等
