import re
x = re.compile(r'(.*?)(?:\s+\(unwanted static pattern\))?$')
for s in ['This will be captured (unwanted static pattern)',
'This wil also be captured']:
m = x.search(s)
if m:
print(m.group(1))
aW1wb3J0IHJlCgoKeCA9IHJlLmNvbXBpbGUocicoLio/KSg/OlxzK1wodW53YW50ZWQgc3RhdGljIHBhdHRlcm5cKSk/JCcpCmZvciBzIGluIFsnVGhpcyB3aWxsIGJlIGNhcHR1cmVkICh1bndhbnRlZCBzdGF0aWMgcGF0dGVybiknLAogICAgJ1RoaXMgd2lsIGFsc28gYmUgY2FwdHVyZWQnXToKICAgIG0gPSB4LnNlYXJjaChzKQogICAgaWYgbToKICAgICAgICBwcmludChtLmdyb3VwKDEpKQ==