text = "1538 a\n123\nskua456\n789\n5\ng\n15563 blu55g\nb\n456\n16453 a\n789\n5\n16524 blu\ng\n55\n1734 a\n987\n987\n55\naasf\n552\n18278 blu\nttry"
f = False
result = []
block = []
for line in text.splitlines():
if 'a' in line:
f = True
if f:
block.append(line)
if 'blu' in line and f:
f = False
result.append("\n".join(block))
block = []
print(result)
dGV4dCA9ICIxNTM4IGFcbjEyM1xuc2t1YTQ1NlxuNzg5XG41XG5nXG4xNTU2MyBibHU1NWdcbmJcbjQ1NlxuMTY0NTMgYVxuNzg5XG41XG4xNjUyNCBibHVcbmdcbjU1XG4xNzM0IGFcbjk4N1xuOTg3XG41NVxuYWFzZlxuNTUyXG4xODI3OCBibHVcbnR0cnkiCmYgPSBGYWxzZQpyZXN1bHQgPSBbXQpibG9jayA9IFtdCmZvciBsaW5lIGluIHRleHQuc3BsaXRsaW5lcygpOgoJaWYgJ2EnIGluIGxpbmU6CgkJZiA9IFRydWUKCWlmIGY6CgkJYmxvY2suYXBwZW5kKGxpbmUpCglpZiAnYmx1JyBpbiBsaW5lIGFuZCBmOgoJCWYgPSBGYWxzZQoJCXJlc3VsdC5hcHBlbmQoIlxuIi5qb2luKGJsb2NrKSkKCQlibG9jayA9IFtdCgpwcmludChyZXN1bHQpCgkJ